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diff --git a/old/62923-0.txt b/old/62923-0.txt deleted file mode 100644 index bc2c2ef..0000000 --- a/old/62923-0.txt +++ /dev/null @@ -1,16072 +0,0 @@ -The Project Gutenberg EBook of The Rare Earths, by S. I. Levy - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org/license - - -Title: The Rare Earths - Their Occurrence, Chemistry, and Technology - -Author: S. I. Levy - -Release Date: August 13, 2020 [EBook #62923] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE RARE EARTHS *** - - - - -Produced by deaurider, Harry Lamé and the Online Distributed -Proofreading Team at https://www.pgdp.net (This file was -produced from images generously made available by The -Internet Archive) - - - - - - - - Transcriber’s Notes - - Text printed in italics has been transcribed _between underscores_, - bold face text ~between tildes~. Small capitals have been replaced - with ALL CAPITALS. _{text} and ^{text} represent subscript and - superscript texts respectively. - - More Transcriber’s Notes may be found at the end of this text. - - - - -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. Photog._ Bulletin de la Société française de - 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. Soc._ Journal of the Physical and Chemical - Society 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. Observ. Publikationen des Astrophysikalischen - Potsdam_ Observatoriums zu Potsdam. - - _Schweigg._ J. Schweigger’s Journal für Chemie und - Physik. - - _Sitzungsber. kaiserl. Akad. Sitzungsberichte der kaiserlich Akademie - Wiss. Wien_ der Wissenschaften zu Wien. - - _Sitzungsber. königl. Akad. Sitzungsberichte der königlich Akademie - Preussischen Wiss. Berlin_ der Wissenschaften zu Berlin. - - _Stahl Eisen_ Stahl und Eisen. - - _Trans. Amer. El. chem. Soc._ Transactions of the American - Electrochemical Society. - - _Trans. Amer. Inst. Min. Transactions of the American Institute - Eng._ of 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. Chem._ Zeitschrift für physikalische Chemie, - Stöchiometrie und Verwandtschaftslehre. - - _Zeitsch. pr. Geol._ Zeitschrift für praktische Geologie. - - _Zeitsch. wiss. Photochem._ Zeitschrift für wissenschaftliche - Photographie, 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._ - - - - -THE RARE EARTHS - - - - -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._ - - 3ThO₂,[3SiO₂,P₂O₅]6H₂O; traces of Fe, Ca, Mg, Al, CO₂, etc. SiO₂ - replaced by P₂O₅/3? ThO₂ = 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.~ - - 3H₂0, 2R´´O, 3R´´´₂O₃, 4SiO₂, where R´´ = Ca, Mg, Th/2; R´´´ = E, Al, - Fe, Mn. E₂O₃ = 40%. - - 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.~ - - _n_CaF₂ + _m_YF₃ 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 {h̅kl}. - - 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. - -[Illustration: 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_ - - _i.e._ ∷ √3/2 : √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,Th/2)--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,R^{iv}O₂,3R´´´₂O₃,16TiO₂,6H₂O, where R´´ = (Ca,Pb,Fe), R^{iv} = -(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´´Fe^{iv}O₃, analogous to Fe´´Ti^{iv}O₃, -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 -(_m_FeTiO₃ + _n_Fe₂O₃ 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(TaO₃)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 U^{iv}(U^{vi}O₄)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. - -[Illustration: 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: - - ELEMENT ATOMIC WT. COLOUR OF SALTS - {Scandium, Sc 44·1 Colourless - {Yttrium, Yt 89·0 Colourless - - {Lanthanum, La 139·0 Colourless - {Cerium, Ce 140·25 Cerous, colourless; ceric, - Cerium { orange to red - Group. {Praseodymium, Pr 140·6 Green - {Neodymium, Nd 144·3 Red to reddish-violet - {Samarium, Sa 150·4 Topaz yellow - - Terbium {Europium, Eu 152·0 Faint rose - Group. {Gadolinium, Gd 157·3 Colourless - {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: - - Element Melting-point Specific 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 + _x_H₂O 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, - Ce^{iv}. - - [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,_x_H₂O, 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. - -[Illustration: 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,_x_H₂O. 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,_x_H₂O, 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,_x_H₂O. 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: - - Element. Equivalent. Atomic 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. - -[Illustration: - - +---------+--------+--------+--------+--------+--------+--------+ - | 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 | | - +---------+--------+--------+--------+--------+--------+--------+ - | „ 4| |K |Ca |_Eka- |Ti | | - | | | | |boron_ | | | - | „ 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. - -[Illustration: 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.] - -[Illustration: - - +---------+--------+--------+--------+--------+--------+--------+ - | 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. - -[Illustration: 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 magnetisation - Element. Atomic Weight. for the oxide. - _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 N/2 -sulphuric acid, in a conical flask of Jena glass. The excess of acid is -titrated with N/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 -HCe^{iii}Ce^{iv}(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: - - [230] _Die Spektren der Elemente, etc._, Leipzig and Vienna, 1911. - - [231] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, II_a_, - 531. - - [232] _Astrophys. J._ 1909, ~29~, 352. - - 4150·11 - 4186·78 - 4222·78 - 4296·88 - 4337·96 - 4382·32 - 4386·95 - 4460·40 - 4479·52 - 4487·06 - 4527·51 - 4528·64 - 4539·90 - 4562·52 - 4572·45 - 4594·11 - 4628·33 - 5512·72 - -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. - -[Illustration: ~GROUP A~ - -MIXED DOUBLE NITRATES. - - 2R(NO₃)₃,3Mg(NO₃)₂,24H₂O. - ||| - +--------------------------------+|| - | +---------------+|+---------------+ - | | | | - ~1~ ~2~ ~3~ ~4~ - La, Pr Pr, Nd Crude Nd Mother-liquors. - Compounds. Compounds. Compounds. - Fractionate as Fractionate as Continue the Sa, Eu, Gd, etc. - R(NO₃)₃,2NH₄NO₃, 2R(NO₃)₃, Separation. Crystallise with - 4H₂O. 3Mn(NO₃)₂,24H₂O. | Bismuth magnesium - | | | nitrate. - | | +-------+ | | | | | - +-------------+ +---------+-------------+| | Terbium - | | | || | elements. - | | | || | - | | | || +---+ - | | | || | - ~5~ ~6~ ~7~ ~8~ ~9~ - Pure ~La~ Pr with La. Impure Pr Pure ~Nd~ Pure ~Sa~ - Compound. Compound. Compound. Compound. - Refine by Continue. Continue. Refine by - Sulphate | | Sulphate - crystallisa- | | crystallisa- - tion. | | tion. - | | - +--------+-----+ +----+ - | | | - Mixture of ~Pr.~ - Pr, La. 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,_n_H₂O 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 - 3988·69 - 4238·55 - 4333·98 - 6250·14 - 6262·52 - 6394·46 - - 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~, II_a_, 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: - - [266] _Zeitsch. wiss. Photochem._ 1906, ~3~, 411. - - 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: - - [267] Exner and Haschek; Bertram, _Zeitsch. wiss. Photochem._ 1906, - ~3~, 16; Eder and Valenta, _Sitzungsber. kaiserl. Akad. Wiss. Wien_, - 1910, ~119~, II_a_, 65. - - 4008·90 - 4100·91 - 4118·70 - 4143·33 - 4179·60 - 4189·70 - 4206·88 - 4223·18 - 4225·50 - 4241·20 - 4305·99 - 4429·38 - 4496·60 - 4510·32 - - -~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: - - [288] _Zeitsch. anorg. Chem._ 1907, ~53~, 83. - - 677·5 - 621·7 - 578·5 } In concentrated solution - 575·4 } these give the - 573·5 } intense absorption - 571·6 } region in the yellow. - 532·3} - 521·6} In concentrated - 520·4} solution these - 512·4} give one intense - 508·7} band. - 474·5 - 468·7 - 461·0 - 427·1 - - The arc spectrum is given by Exner and Haschek, Bertram,[289] and - Eder and Valenta.[290] The most intense lines are as follows: - - [289] _Zeitsch. wiss. Photochem._ 1906, ~3~, 16. - - [290] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, II_a_, - 554. - - 3863·52 - 3951·32 - 4061·27 - 4156·30 - 4247·54 - 4282·67 - 4303·78 - 4325·87 - 4375·11 - 4385·81 - 4400·96 - 4446·51 - 4451·71 - 4463·09 - 4920·84 - 5923·35 - 5319·98 - 5594·58 - 5620·75 - 6310·69 - 6314·69 - 6385·32 - - -~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 - 463 - 417 - 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 - 4152·38 - 4203·18 - 4225·48 - 4229·83 - 4236·88 - 4256·54 - 4319·12 - 4329·21 - 4334·32 - 4347·95 - 4391·03 - 4420·72 - 4421·32 - 4424·55 - 4434·07 - 4434·52 - 4452·92 - 4454·84 - 4458·70 - 4467·50 - 4519·80 - 4524·08 - 4544·12 - 4566·38 - 4577·88 - 4642·41 - 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, Y_{α} and -Y_{β} from the same mineral; Y_{β} was afterwards found to be identical -with samaria, whilst Y_{α} 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 Z_{ξ} and Z_{ε}. In 1896, -Demarçay[308] separated an earth Σ, which showed the spark-spectrum of -Z_{ε} and the reversal spectrum of Z_{ξ}, 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 Z_{ε}. The reversal - spectrum shows the characteristic band of Z_{ξ}. - - 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: - - [321] Exner and Haschek; Eder and Valenta, _Sitzungsber. kaiserl. - Akad. Wiss. Wien_, 1910, ~119~, II_a_, 31. - - [322] _Proc. Roy. Soc._ 1907, ~79~; A, 118. - - 3688·57 - 3725·10 - 3819·80 - 3907·28 - 3930·66 - 3972·16 - 4129·90 - 4205·20 - 4435·75 - 4522·76 - 4594·27 - 4627·47 - 4662·10 - 6645·44 - - -~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 Y_{α}, 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: - - [332] Urbain, _ibid._ 1905, ~140~, 1233. - - [333] Exner and Haschek; Eder and Valenta, _Sitzungsber. kaiserl. - Akad. Wiss. Wien_, 1910, ~119~, II_a_, 21. - - 3082·15 - 3100·66 - 3422·62 - 3545·94 - 3549·52 - 3585·12 - 3646·36 - 3671·39 - 3719·63 - 3743·68 - 3768·60 - 3796·62 - 3814·18 - 3852·65 - 3916·70 - 4037·49 - 4050·05 - 4063·62 - 4070·51 - 4073·99 - 4085·73 - 4098·80 - 4130·59 - 4184·48 - 4251·90 - 4262·24 - 4325·83 - 4327·29 - 4342·35 - 6114·26 - - 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 Z_{δ} and Z_{β} of de Boisbaudran,[342] with the Γ of -Demarçay,[343] and with the G_{β} and possibly the G_{ζ} 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, Z_{δ} (_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 - Z_{β} 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 - 3676·52 - 3703·05 - 3704·01 - 4005·62 - 4278·71 - - The chief lines in the arc spectrum (Exner and Haschek) are the - following: - - 3324·53 - 3509·34 - 3531·86 - 3561·90 - 3568·69 - 3600·60 - 3628·53 - 3650·60 - 3659·02 - 3704·10 - 3711·91 - 3848·90 - 3874·33 - 3899·34 - 3925·60 - 3939·75 - 3977·01 - 3982·07 - 4005·70 - 4012·99 - 4278·70 - 4752·69 - - 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, - G_{β}. 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~, II_a_, - 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. - -[Illustration: ~GROUP B~ - -YTTRIUM DOUBLE SUPLHATES. - - Fractionate as Bromates. - ||||| - +--------------------------+|||+-------------------------+ - | +------------+|+------------+ | - | | | | | - ~1~ ~2~ ~3~ ~4~ ~5~ - Gd, Tb, Dy. Tb, Dy, Ho, Dy, Ho, Er, Yt, Er, and Tm, Yb, Lu, - Yt. Yt. Sc? etc. - For separa- Transform to Fractionate Fractionate Continue. - tion of Ethyl- by Nitrate by Nitrate ||||| - Terbium sulphates. Fusion. Fusion. ||||| - group.--+ ||| || || ||||| - | | | | ||| +---+| || ||||| - Terbium | ||| | | || ||||| - Group. | ||| | | ||+----------+|||| - +----+ ||| | |+-----------+|| +---+||| - |+----------+|| | || +-----+| | ||+-----+ - || +-----+| | || | | | |+-----+| - ~6~ | ~8~ | ~10~ | ~12~ | ~14~ || - Tb, Dy. | Ho, Yt. | Yt, Er. | ~Tm.~ | ~Lu.~ || - Continue | Fractionate | Continue. | Bromate. | Bromate.|| - Ethylsulphate| by Nitrate | | | || - Fractiona- | Fusion. | | | +----+| - tion. | | | | | | +---+ - | | | | | | | - ~7~ | ~9~ ~11~ ~13~ | | - ~Dy.~ | ~Yt.~ ~Er.~ ~Yb.~ | | - Ethylsulphate.| Nitrate. Nitrate. Bromate. | | - | +---------+ + - +----------+ | | - | | Yb, Lu. Ct? - | | Bromates. Bromate. - ~Ho.~ Ho, Yt. - Basic Nitrate. - -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 - 3531·86 - 3536·17 - 3645·54 - 3898·69 - 3944·83 - 4000·59 - 4078·11 - 4187·00 - 4211·82 - - [368] _Publ. astrophys. Observ. Potsdam_, 1909, ~20~, No. 60. - - See also Exner and Haschek, and Eder and Valenta.[369] - - [369] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, II_a_, 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 - 654 strong - 541 very weak - 523 very strong - 519 shadowy - 492 - 487 strong - 450 - 442 weak - - [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 - 3264·91 - 3312·56 - 3372·92 - 3499·28 - 3692·85 - 3896·40 - 3906·47 - 3938·79 - - [382] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, II_a_, - 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~, II_a_, - 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~, II_a_, - 1123. - - [395] _Ibid._ 1910, ~119~, II_a_, 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~, II_a_, 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 - 2469·3 - 2481·6 * - 2536·9 * - 2677·7 - 2685·2 ** - 2729·1 * - 2737·9 - 2765·8 ** - 2834·3 * - 2837·3 * - 2845·2 * - 2870·2 - 2885·1 * - 2903·9 * - 2931·9 - 2949·5 * - 3080·7 ** - 3118·6 ** - 3171·4 * - 3197·9 ** - 3326·0 * - 3391·5 * - 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: - - [418] _Zeitsch. wiss. Photochem._ 1909, ~7~, 245. - - [419] _Sitzungsber. kaiserl. Akad. Wiss. Wien_, 1910, ~119~, IIa, 1. - - 3216·83 - 3242·42 - 3328·02 - 3600·92 - 3611·20 - 3621·10 - 3633·28 - 3664·78 - 3710·47 - 3774·52 - 3788·88 - 3950·52 - 3982·79 - 4077·54 - 4102·57 - 4128·50 - 4143·03 - 4177·74 - 4302·45 - 4309·79 - 4348·93 - 4375·12 - 4883·89 - 6191·91 - 6435·27 - - 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~, II_a_, - 576. - - The most intense lines of the arc spectrum are the following: - - 3353·90 - 3372·33 - 3558·69 - 3567·89 - 3572·73 - 3576·53 - 3614·00 - 3630·93 - 3642·99 - 3907·69 - 3912·03 - 4020·60 - 4023·88 - 4247·02 - 4314·31 - 4320·98 - 4325·22 - 4374·69 - 4400·63 - 4415·78 - 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 neutral chlorides cannot be obtained -from solution. As is to be expected from its high atomic weight, thorium -approaches most nearly to the rare earths in chemical properties; thus -it forms stable double nitrates of the type R₂Th(NO₃)₆ and its salts, -especially the sulphate, resemble those of the rare earth elements in -their solubility relations. - -The elements titanium, zirconium, and thorium are distinguished also by -the fact that they form no definite hydroxides. The precipitates thrown -down from solutions of the salts, on addition of alkali, are hydrated -oxides, which lose water continuously when dried, giving rise to no -definite chemical individuals until constant weight is reached with the -anhydrous oxides. The hydroxides have the further characteristic, common -also to the other members of Group IV, of readily forming colloidal -solutions and gels, a property possessed to some extent also by the -elements themselves, and particularly by zirconium, which, when reduced -from its compounds, shows a great tendency to go into colloidal solution -merely on washing. Highly characteristic also is the property of forming -‘meta’-oxides (acids) and ‘meta’-salts, which is common to all the Group -IV elements which have solid oxides. - -In presence of hydrogen peroxide, alkalies throw down characteristic -hydrated peroxides, which have definite acidic properties in the case of -titanium: the zirconium compound is less strongly acidic, the cerium -compound shows no tendency to salt formation, whilst if hydrogen -peroxide be added to a neutral or faintly acid solution of a thorium -salt, the precipitate is a peroxy-salt, containing some acid grouping, -_e.g._ SO₄,NO₃. - -With regard to valency, the elements in the typical compounds are -tetravalent. Titanium forms three series of salts, in which the element -is respectively di-, tri-, and tetravalent; salts of the first two -series have powerful reducing properties, and the compounds in which -the metal is tetravalent are most stable. Zirconium is always, with the -doubtful exception of its peroxy-compounds and the lower oxides, -tetravalent. Cerium, as already described, can form two series of -compounds, in which it is respectively tri- and tetravalent; thorium, -like zirconium, is always tetravalent. - - -~Titanium~, Ti = 48·1 - -Though generally classed among the rare elements, titanium is probably -at least as widely distributed in nature as most of the common metals. -It occurs as the dioxide in small quantities in all the common silicate -rocks and minerals, and in traces in the animal and vegetable kingdoms; -the element has been identified in the sun and in many stars, and has -been found in meteorites. Probably the commonest mineral in which the -element occurs in quantity is ilmenite, or titaniferous ironstone, which -occurs in enormous quantities in many parts of the world (see p. 57). -The pure dioxide occurs in the three forms Rutile, Brookite, and Anatase -(_q.v._), in which it is said to be isotrimorphous with tin dioxide. -Other important titanium minerals are Perovskite, Titanite or Sphene, -the Euxenite series, and other minerals of the tantalo-columbate group -(see Part I). - -The commercial sources of titanium compounds are the minerals rutile and -ilmenite. These may be opened up by fusion with alkali or alkali -carbonate; the residue after extraction with water is dissolved in acid, -and precipitated with ammonia; the mixture of iron and titanium oxides -thrown down may be separated by one of the methods outlined on p. 339. -Fusion with potassium bisulphate has also been employed. A very -satisfactory method is that of Stähler,[437] in which the ore is fused -with carbon in the electric furnace. The carbides so obtained are heated -in a stream of chlorine, when the volatile titanium tetrachloride -distils over, and may be obtained quite pure by redistillation; by -appropriate methods, the required compounds may be obtained from this. -(See also pp. 326-7.) - - [437] _Ber._ 1904, ~37~, 4405; 1906, ~38~, 2619. - -_The Metal._--The difficulty of isolating metallic titanium in the pure -state is very great, on account of its great affinity for nitrogen, -oxygen, hydrogen, carbon, etc., the ease with which it forms alloys with -all the common metals, and the extremely high melting-point; in -consequence, it is only within recent times that the element has been -obtained in a state approximately approaching purity, and the accounts -given of its physical properties vary very widely. - -Berzelius prepared an impure titanium (Ti = 86 per cent.) by reduction -of potassium titanofluoride with potassium; the method was modified by -Wöhler, who heated a tube containing two boats, of which one was filled -with the fluoride, the other with sodium, reduction being effected by -the sodium vapour. Many authors have attempted the reduction of titanium -tetrachloride by means of hydrogen. By heating the tetrachloride with -sodium in a cast iron bomb, Nilson and Pettersson obtained a product -containing 95 per cent. of the element. Reduction of the dioxide by -means of sodium, magnesium, silicon, or aluminium has not been found to -yield good results, by reason of the ease with which titanium alloys -with these elements. Reduction of the dioxide with carbon yields good -results only when precautions are taken to avoid the formation of the -compound which the element so readily forms with carbon and nitrogen. -Moissan[438] found that if temperatures high enough to decompose this -compound were used, the product contained as the only impurity carbon, -which could be partly removed by fusing with the dioxide; the product -then contained 98 per cent. of titanium. - - [438] _Compt. rend._ 1895, ~120~, 290. - -The element has been obtained in the fused condition by Weiss and -Kayser,[439] who pressed the amorphous form into sticks, under a -pressure of 70,000 atmospheres, and employed these as pencils for the -electric arc _in vacuo_; the metal fused, forming globules on the ends -of the electrodes, which were detached after the apparatus had been -allowed to cool. - - [439] _Zeitsch. anorg. Chem._ 1910, ~65~, 388. - -The amorphous element is a dark powder, resembling finely divided iron -(Ferrum reductum), of density 3·5-3·6. The specific heat rises rapidly -with the temperature, so that the atomic heat has the values 5·40 -between 0° and 100°, 6·18 between 0° and 210°, 7·13 between 0° and 300°, -and 7·77 between 0° and 440°. The amorphous element is said to be -paramagnetic. - -The fused carbonaceous product of Moissan formed an extremely brittle -mass, with a shining white lustre on the fractured surface, sufficiently -hard to scratch quartz and steel; its density was determined as 4·87. -The product of Weiss and Kayser was also extremely hard and brittle; -when rubbed against steel, it gave bright sparks. Its density was found -to be 5·174, and the heat of combustion for the gram-atom, 97·79 K. - -The amorphous variety is fairly stable in air, but burns vigorously when -heated in air, oxygen, or halogens. Heated in nitrogen or ammonia, it -reacts vigorously, forming the nitride TiN; if carbon is present, a -peculiar substance of uncertain composition, known as _titanium -cyanonitride_, is formed. This substance is also obtained when air is -passed over a heated mixture of the dioxide with coke, and is found in -blast-furnaces in which ores containing small quantities of titanium are -worked; it forms brilliant red cubes, which are extremely hard and -resistant to acids. This substance, as well as the nitride itself, -yields ammonia when heated in steam, and has been proposed as a medium -for ‘fixing’ atmospheric nitrogen (see p. 337). - -The amorphous element also absorbs hydrogen, when heated in the gas, but -no definite hydride is known. It combines when heated with almost all -the known non-metals, and forms alloys with all the common metals. -Moissan[440] claims to have prepared a compound as hard as diamond by -heating titanium with boron in the electric furnace. The element attacks -steam at a red heat. - - [440] _Loc. cit._ - -The element is fairly resistant to acids in the cold, but is readily -attacked, with evolution of hydrogen, on warming. Hot dilute -hydrochloric acid gives the trichloride; but dilute sulphuric acid is -variously reported to give the di- and tri-salt. Hot nitric acid -oxidises it readily, forming the so-called metatitanic acid. -Hydrofluoric acid attacks it very readily, forming the tetrafluoride. - - -COMPOUNDS OF DIVALENT TITANIUM. - -The compounds of divalent titanium show resemblances to those of -divalent iron, chromium and vanadium, but on account of the great -difficulty of preparing them and protecting them from oxidation, little -is known of their properties and behaviour; even the colour of the salts -in solution is not known with certainty. In its divalent state; the -element does not appear to act as a strongly positive metal; the salts -in solution are said to show an acid reaction, whilst the precipitates -thrown down with alkali oxalates and acetates are soluble in excess of -the precipitant, forming deeply coloured solutions. With sodium -phosphate the soluble salts give a bluish-black precipitate, with -potassium ferrocyanide and ferricyanide, dark brown and reddish-brown -precipitates respectively. They are distinguished from salts of the -higher oxides of titanium by the brown colouration produced by potassium -thiocyanate in presence of hydrochloric acid.[441] - - [441] v. d. Pfordten, _Annalen_, 1886, ~234~, 257; 1887, ~237~, 201; - see also _Ber._ 1889, ~22~, 1485. - -The _hydroxide_ is thrown down from solutions by addition of alkali, -alkali carbonate, alkali cyanide, or ammonium sulphide, as a black -precipitate. It cannot be transformed to the corresponding oxide by -drying, since it attacks the water with evolution of hydrogen, forming -the dioxide. The _monoxide_, TiO, has probably never been obtained in -the pure state; it is formed by reduction of the dioxide with zinc or -magnesium. Moissan[442] obtained it in the form of black prismatic -crystals by treating the dioxide with the calculated amount of charcoal -in the electric furnace. The _sulphide_, TiS, is an extremely stable -compound; it can be prepared by heating the higher sulphides in a stream -of hydrogen to a very high temperature, and then forms pseudomorphs -after these.[443] It is a dark red metallic mass, which reacts in the -air only when heated, forming the dioxide; dilute acids and alkalies -have no action on it, concentrated nitric acid oxidises it slowly. - - [442] _Loc. cit._ - - [443] See v. d. Pfordten (_loc. cit._); Thorpe, _Chem. News_, 1885, - ~51~, 260. - -The _dichloride_, TiCl₂, is obtained in the impure state as a black -powder by decomposition of the trichloride at a red heat: the -tetrachloride is formed at the same time, and volatilises.[444] -According to v. d. Pfordten,[445] it is obtained by reduction of the -tetrachloride by sulphuretted hydrogen or sodium amalgam in the cold. -The latter author states that it dissolves in alcohol or water in -absence of air to a dark brown solution; Friedel and Guérin, however, -state that it acts energetically on these solvents with evolution of -hydrogen, forming a yellow solution. When heated in the air it burns, -evolving fumes of the tetrachloride and leaving a residue of the -dioxide. The _iodide_, TiI₂, has been obtained by Defacq and Copaux[446] -by reduction of the tetraiodide with silver or mercury, as a black, -lustrous, infusible sublimate. It is insoluble in organic solvents, but -reacts with water and aqueous alkalies, and is readily attacked by -acids. Hydrogen at a bright red heat reduces it to amorphous titanium. - - [444] Friedel and Guérin, _Compt. rend._ 1875, _81_, 889; 1876, ~82~, - 509, 872. - - [445] _Loc. cit._ - - [446] _Compt. rend._ 1908, ~147~, 65. - - -COMPOUNDS OF TRIVALENT TITANIUM.[447] - - [447] Compounds of trivalent titanium are frequently referred to in - English chemical and technical literature as ‘Titanous Compounds,’ the - salts of the tetravalent element being tacitly recognised as ‘Titanic - Compounds.’ In view of the existence of compounds of divalent - titanium, to which the name ‘Titanous Compounds’ might be more - logically applied, the former nomenclature cannot be regarded as - altogether satisfactory, and it is therefore not adopted here. - -These salts are obtained when the element is dissolved in hydrochloric -and sulphuric acids, and by reduction of the compounds of tetravalent -titanium in solution by means of zinc and hydrochloric acid, or by -electrolysis. According to Diethelm and Forster[448] the reduction may -also be effected by hydrogen in presence of finely divided platinum. The -salts have strong reducing properties, transforming nitro-bodies to -amines and decolourising azo-derivatives very rapidly; they reduce -unsaturated bodies, and reduce dyes to the leuco-bases; they reduce -sulphurous acid to sulphur, precipitate gold, silver and mercury from -their salts, and reduce cupric and ferric salts to cuprous and ferrous -compounds respectively. The salts are green or violet in solution, -showing the phenomenon of hydrate-isomerism which is exhibited by the -chromic salts; they are to some extent hydrolysed in aqueous solution, -as shown by the acid reaction of the chloride. They resemble the salts -of ferric iron and aluminium in giving precipitates of basic salts when -boiled with sodium acetate or sodium formate, and in giving no -precipitate with alkalies in the presence of organic hydroxy-acids. -Ferrocyanide and ferricyanide give brown precipitates. - - [448] _Zeitsch. physikal. Chem._ 1908, ~62~, 129. - -The _hydroxide_, Ti(OH)₃,_x_H₂O, is thrown down as a dark precipitate -with strong reducing properties; it attacks water with evolution of -hydrogen, forming the dioxide; when an aqueous suspension is shaken with -air, autoxidation occurs, hydrogen peroxide being formed. The -_sesquioxide_, Ti₂O₃, has been prepared by Friedel and Guérin[449] by -heating the dioxide to a white heat in a current of hydrogen and -titanium tetrachloride; it forms black lustrous crystals, isomorphous -with hæmatite. The _sulphide_, Ti₂S₃, is best obtained by reduction of -the disulphide, at a moderate temperature, in a stream of hydrogen or -nitrogen, but is also prepared by the action of a mixture of carbon -disulphide and sulphuretted hydrogen on the dioxide at a high -temperature. It is a dark grey metallic powder, stable towards air, -water, alkalies and dilute acids. - - [449] _Loc. cit._ - -_Titanium Nitride_, TiN, is obtained in all reduction processes in which -titanium compounds are used, if air or nitrogen is admitted; it is -formed when the element is heated in nitrogen, and by the action of -ammonia on the chloride. It forms lustrous, bronze-coloured leaflets, -which appear blue or violet when powdered. It is extremely hard, and -very stable, but is attacked by alkalies with evolution of ammonia. It -reduces the oxides of copper and lead in the fused state. Ruff and -Eisner have shown that it is a true nitride of the trivalent element, -and that only one nitride exists.[450] - - [450] _Ber._ 1905, ~38~, 742; 1908, ~41~, 2250. - -The _fluoride_, TiF₃, has been obtained as an insoluble violet powder by -reduction of potassium titanofluoride, K₂TiF₆, with hydrogen. From a -solution it may be obtained by reduction of the same salt with zinc and -hydrochloric acid, or sodium amalgam. It forms complex salts with alkali -or ammonium fluoride, of which the compound (NH₄)₃TiF₆ is an example; -this salt appears to be isomorphous with the analogous compounds, -(NH₄)₃VF₆, (NH₄)₃CrF₆, and (NH₄)₃FeF₆. By autoxidation in the air, the -solutions form fluoroxypertitanates. The complex salts appear to exist -in two forms, a violet insoluble form and a green soluble modification. - -The _chloride_, TiCl₃, is obtained anhydrous by reduction of the -tetrachloride--mercury, silver, and hydrogen being the most suitable -agents. Heated in hydrogen, it breaks up, forming the tetrachloride and -the dichloride; heated in air it burns, evolving the tetrachloride and -leaving a residue of dioxide. In solution, in combination with alkali -chlorides, and as the solid hydrate, it exists in the green and violet -forms. Concentrated aqueous solutions deposit the violet hexahydrate, -TiCl₃,6H₂O. If such a solution be covered with ether, and saturated at -0° with hydrogen chloride, the green modification is formed, and may be -extracted by the ether; it is stable only in the presence of -hydrochloric acid. In the violet form, all the chlorine is in the ionic -condition, and can be removed by silver nitrate; similar determinations -have not been made with the green form, but it is most probable, as in -the case of the analogous chromic salts, that only part of the chlorine -content can be removed by silver nitrate. Böck and Moser[451] have -recently described a brown substance, obtained by the action of the -silent electric discharge on a mixture of hydrogen and the vapour of -titanium tetrachloride at the ordinary temperature, which they believe -to be a monotropic modification of the ordinary violet trichloride; the -change of this brown form to the violet form is irreversible. - - [451] _Monats._ 1912, ~33~, 971; 1913, ~34~, 1825. - -The _bromide_ and _iodide_ resemble the chloride, but are very unstable. - -The _sulphate_, Ti₂(SO₄)₃, is obtained as a green crystalline powder by -heating with sulphuric acid the violet solution obtained by reduction of -a solution of the dioxide in sulphuric acid. It dissolves in dilute -acids, forming violet solutions. With alkali sulphates it forms -_titanium alums_, which can be recrystallised from dilute sulphuric -acid, and have the general formulae, properties, and crystal form of the -other alums. An _acid sulphate_, 3Ti₂(SO₄)₃,H₂SO₄,25H₂O, is obtained by -electrolytic reduction of a strongly acid solution of the dioxide in -sulphuric acid, or by treating the chloride repeatedly with hot dilute -sulphuric acid. It forms a crystalline violet powder, with silky lustre, -insoluble in alcohol, ether, and 60 per cent, sulphuric acid; it -dissolves slowly in water, forming a violet solution. When the aqueous -solution is treated with excess (2¹⁄₂ molecules) of alkali sulphate, it -forms sparingly soluble _double sulphates_, which separate in bright -blue crystals; the compounds Ti₃(NH₄)(SO₄)₅,9H₂O, and Ti₃Rb(SO₄)₅,12H₂O, -have been obtained in this way. - -_The Use of Salts of Trivalent Titanium in Volumetric Analysis._--Owing -to their powerful reducing properties, these salts have been proposed as -very convenient reagents in volumetric analysis,[452] the chloride being -most useful in this respect. The estimations must be carried out in -absence of air, to avoid atmospheric oxidation; generally the apparatus -is filled with carbon dioxide. The titanium solutions for use must also -be preserved from the oxidising action of the air. - - [452] See Knecht, _Ber._ 1903, ~36~, 166; Knecht and Hibbert, _ibid._ - 1903, ~36~, 1549; 1905, ~38~, 3318; 1907, ~40~, 3819. - -For estimation of ferric salts, an aliquot quantity is titrated directly -with the titanium solution, ammonium thiocyanate being used as -indicator. Ferrous salts and ferric salts in the same solution are -easily estimated by titrating the former with permanganate solution, or -better with hydrogen peroxide, and then estimating the total ferric salt -with the titanium solution. Oxidising agents like nitrates and chlorates -can be estimated in acid solution by treatment with an excess of a -ferrous salt, and estimation of the ferric compound formed by means of -titanium. Azo-bodies and organic dyes can be titrated directly, if -soluble in hydrochloric acid, the disappearance of colour marking the -end of the reaction; nitroso-compounds can also be estimated in this -way. If the compound is insoluble, it may be reduced in hydrochloric -acid suspension with excess of the titanium salt, and the excess then -determined by means of ferric iron. Insoluble dyes may also be converted -into soluble sulphonic acids, and estimated directly in solution. -Ammonium persulphate may be estimated by reduction with excess of the -chloride, and back titration of the excess with ferric iron. Hydrogen -peroxide may be estimated directly, the disappearance of the yellow -colour formed at the first addition marking the end of the reaction. Tin -may be estimated by addition of an excess of a ferric salt, and -estimation of the excess by titanium in the usual way. Cupric salts also -may be estimated directly,[453] the end point being reached when the -bluish-green solution becomes colourless. - - [453] Moser, _Chem. Zeitg._ 1912, ~36~, 1126. - - -COMPOUNDS OF TETRAVALENT TITANIUM - -The compounds of tetravalent titanium are much more stable than the -compounds in which the element has a lower valency, and are very readily -formed from them. The dioxide is amphoteric in character, and acts as a -weak acid as well as a weak base; the salts it forms with acids as well -as those it forms with bases are very easily hydrolysed, with separation -of the hydrated oxide. Titanium salts, therefore, can only be held in -solution by a considerable excess of acid. The tendency to the formation -of complex compounds is very pronounced, particularly in the case of the -fluoride, oxalate and tartrate. - -The _hydroxide_, or _hydrated oxide_, is capable of existing in two -modifications, according to the conditions under which it is thrown -down, though the two can hardly be said to be very definitely -differentiated. The α or ortho form is obtained as a voluminous white -precipitate by the addition of ammonia or alkali hydroxide in the cold -to a freshly prepared solution of a titanium salt. It is insoluble in -water and alcohol, but dissolves readily in dilute mineral acids, and to -some extent also in dilute alkalies. The water content is very variable, -and no definite hydrate or hydroxide can be prepared; when the substance -is heated, it loses water continuously, and at a definite temperature -glows, doubtless by reason of some polymeric change. If it be maintained -for some time at a temperature somewhat below the normal temperature of -glowing, this phenomenon no longer occurs when the temperature is -further raised. - -The β modification, or metatitanic acid, as it is called, is obtained by -hydrolysis of the salts by boiling, or by addition of alkali at 100°, as -a fine white precipitate. It is almost insoluble in dilute acids and -alkalies, but dissolves in water to a colloidal solution; when heated it -does not glow. The β form is also obtained when the metatitanates are -treated with water; these compounds hydrolyse very readily, but the -precipitated dioxide carries down alkali by adsorption. - -The _dioxide_, TiO₂, occurs crystalline in nature in the three forms -Rutile, Brookite, and Anatase, all of which can be prepared by -laboratory methods;[454] the amorphous form is obtained by ignition of -the hydrated oxide, and of suitable salts. The oxide melts at 1560°, -forming a mobile (?) liquid of density 4·1; for the physical properties, -see the accounts of the naturally occurring forms in Chapter V. When -heated in a current of hydrogen or carbon monoxide, it gives rise to -intermediate oxides, Ti₃O₄, Ti₇O₁₂, etc., which are not very well known, -and are of doubtful individuality. It reacts when heated in chlorine, -and with many non-metallic chlorides, forming the tetrachloride; with -carbon disulphide at high temperatures it gives the disulphide, ammonia -at a red heat forms the nitride. It is exceedingly resistant to acids, -but is attacked slowly by boiling sulphuric acid, more quickly by fused -bisulphate. - - [454] See p. 79; also Hautefeuille, _Ann. chim. phys._ 1863, [iv.], - ~4~, 129. - -_Titanium disulphide_, TiS₂, is obtained in the pure state when a -mixture of the vapour of the tetrachloride and sulphuretted hydrogen is -led through a strongly heated porcelain tube. It is a fairly stable -substance, forming metallic crystals which yield the dioxide when heated -in air. When heated in a stream of hydrogen or nitrogen it yields one or -other of the lower sulphides according to the temperature employed. It -is not attacked by water, but dissolves in acids, and is decomposed by -boiling potash, forming a titanate; it is insoluble in alkali sulphides. - -The _carbide_, TiC, was prepared by Moissan by heating the oxide with -carbon in the electric furnace; any excess of carbon separates on -cooling as graphite. It has the density 4·25, and resembles the fused -element in appearance. It dissolves in nitric but not in hydrochloric -acid. - -_Titanium tetrafluoride_, TiF₄, is obtained by the action of fluorine on -the element or the carbide, and by the action of anhydrous hydrofluoric -acid on the element or the tetrachloride. It is a white powder, and -boils at 284°; it is very hygroscopic, and dissolves easily in alcohol -and water, showing little tendency to form basic salts. From the -concentrated aqueous solution it separates as the dihydrate, TiF₄,2H₂O; -basic salts are obtained only by repeated evaporation with water. The -anhydrous compound forms additive products with ammonia and with -pyridine. - -With aqueous hydrofluoric acid it forms the complex H₂TiF₆, as shown by -conductivity measurements, and the fact that only a slow and incomplete -precipitation of the hydroxide is effected by addition of ammonia. The -solution dissolves metallic oxides and carbonates, forming -_titanofluorides_, which are for the most part isomorphous with the -corresponding silicofluorides, stannofluorides, and zirconofluorides. -They are very stable crystalline salts, of the general formula R´₂TiF₆; -many salts of the types R´´TiF₆, R´₃TiF₇, etc., have been prepared. The -most important is the potassium salt, K₂TiF₆, which crystallises from -acid solutions in monoclinic tablets; from aqueous solution it separates -as the monohydrate, K₂TiF₆,H₂O, isomorphous with the compounds -K₂CbOF₅,H₂O and K₂WO₂F₄,H₂O. The hydrate loses its water at 100°, and -melts at a white heat without decomposition. It is moderately soluble in -hot, very sparingly soluble in cold water, and hence is readily -recrystallised. - -The _tetrachloride_, TiCl₄, is important, on account of its low -boiling-point, for the separation and purification of titanium -compounds. In physical as well as chemical properties, it resembles the -chloride of a non-metallic element rather than a normal salt, and is -distinguished by the ease with which it combines or reacts with the most -widely differing organic compounds. It is prepared by the action of -chlorine upon the element, the carbide, or a mixture of the dioxide with -carbon, and by the action of chloroform or carbon tetrachloride upon the -dioxide at a bright red heat. It is a colourless, transparent liquid, of -density 1·76 at 0°; it freezes at -23°, and boils at 136° under -atmospheric pressure. In moist air it fumes excessively, yielding -hydrogen chloride by hydrolysis: TiCl₄ + H₂O = TiOCl₂ + 2HCl, and is -decomposed by water with separation of the hydrated oxide. If the -compound be added slowly to a large quantity of cold water, and the -clear solution warmed, the oxide formed by hydrolysis remains in -colloidal solution. - -The chloride dissolves in fuming hydrochloric acid, forming a deep -yellow solution, which becomes colourless when diluted. The solution -appears to contain the unstable complex acid H₂TiCl₆, or its ions; by -addition of ammonia, or organic bases, salts of the type (NH₄)₂TiCl₆ can -be obtained as yellow crystalline solids. An interesting property of the -chloride is its ability to form stable additive compounds with the -chlorides of negative elements. A long series of these are known, of -which the compounds TiCl₄,PCl₃, TiCl₄,PCl₅, TiCl₄,POCl₃, and -TiCl₄,2POCl₃ may be considered examples; for the most part, they can be -distilled without decomposition. A very long series of compounds, partly -additive and partly condensation products, with all kinds of organic -substances, is also known. - -A series of _oxychlorides_, or _basic chlorides_, TiCl₃(OH), TiCl₂(OH)₂, -and TiCl(OH)₃, has been obtained by addition of hydrochloric acid, in -certain quantities and concentrations, to the chloride; they are -amorphous solids, of which little is known. - -The _tetrabromide_, TiBr₄, is a yellow crystalline solid, melting at 39° -and boiling at 230°. Its solutions in concentrated hydrobromic acid are -of a blood-red colour, and by treatment with ammonia and organic bases -yield deep red crystalline salts of the type (NH₄)₂TiBr₆. The -_tetraiodide_, TiI₄, is a reddish-brown metallic-looking solid, melting -at 150°, and boiling at 360°; no complex salts are known. - -_The sulphates._--Many compounds of doubtful composition and -individuality have been described as titanium sulphates, but relatively -little is known with certainty of this class of derivatives. The most -stable seems to be the _titanyl sulphate_, TiOSO₄, obtained as a white -powder, which is slowly hydrolysed by water, by evaporating a solution -of the dioxide in concentrated sulphuric acid. Under suitable -conditions, _e.g._ when separated from acid or alcoholic solutions, it -is said to form hydrated compounds; the mono-, di- and penta-hydrate -have been described. When solutions of this compound in concentrated -sulphuric acid are treated with concentrated aqueous solutions -of alkali sulphates, salts of the formulæ (NH₄)₂TiO(SO₄)₂,H₂O and -K₄(TiO)₃(SO₄)₅,10H₂O, are obtained. By treating solutions of the dioxide -in a large excess of concentrated acid with solutions of calcium or -strontium sulphate in sulphuric acid, salts of the type R´´Ti(SO₄)₃ are -obtained; the barium salt has the formula 3Ti(SO₄)₂,2BaSO₄. All these -compounds are rapidly hydrolysed by water. - -_Phosphoric Acid Derivatives._--Solutions of titanium compounds are -completely precipitated by the addition of phosphoric acid, or soluble -phosphates, even in presence of a large excess of mineral acid, but the -composition of the precipitate obtained is unknown. By heating the oxide -with orthophosphoric acid, a crystalline compound, TiO₂,P₂O₅, is -obtained, and various alkali double phosphates may be prepared by -suitable fusions. - -Concentrated aqueous oxalic acid solutions readily dissolve one -equivalent of titanium dioxide, forming greenish-yellow solutions which -contain _titanyl oxalate_, TiO(C₂O₄). From alcoholic solution, this -substance can be precipitated by ether as the alcoholate, -TiO(C₂O₄),C₂H₅OH, a micro-crystalline precipitate soluble in water and -alcohol. _Titanyloxalic acid_, TiO(HC₂O₄)₂,H₂O, and its salts are stable -compounds; the latter are obtained by dissolving the dioxide in alkali -binoxalate, the acid itself being obtained by treatment of the sparingly -soluble barium salt with sulphuric acid. - -Complex acids are also formed with tartaric acid, and other organic -hydroxy-acids; from its solutions in these acids, the dioxide cannot be -again precipitated by boiling, or by addition of alkalies. - -_Titanates and Pertitanates._--On account of the weakly acid character -of the dioxide, stable titanates can be prepared only in the dry way. -The dioxide resembles silica in the conditions under which it forms -salts, and in the nature, and generally the crystallographic properties, -of the products obtained. The commonest salts are the metatitanates of -the formulae R´₂TiO₃ and R´´TiO₃, which are obtained by fusing the -dioxide with metallic oxides and carbonates, sometimes with addition of -a suitable agent to act as a crystallising medium, _e.g._ sodium -tungstate, calcium chloride, magnesium chloride, etc. Calcium -metatitanate, CaTiO₃, prepared by heating titanium dioxide with calcium -carbonate in presence of calcium chloride, is identical in properties -with the naturally occurring compound, Perovskite (_q.v._). -Orthotitanates of divalent metals only are known; these have the general -formula R´´₂TiO₄, and are prepared by similar methods. The iron compound -FeTiO₃ is also identical in properties with the mineral ilmenite, and -isomorphous with the sesquioxides Fe₂O₃, Ti₂O₃. Magnesium titanates of -both the ortho type (Mg₂TiO₄) and the meta type (MgTiO₃) have been -prepared in the laboratory; the latter is identical with the mineral -Geikielite (_q.v._). - -The compounds prepared in this way are all insoluble in water, doubtless -by reason of the slowness with which such compact solids can be -attacked; they dissolve easily in dilute acids. The weakly acid -character of titanium dioxide is shown by the fact that if the fusion -with metallic carbonates be carried out in vessels so adjusted that the -carbon dioxide exerts a pressure of one atmosphere, a condition of -equilibrium is reached, in which a considerable part of the carbonate -remains unattacked. In the presence of hydrogen peroxide, however, the -acidic properties are considerably strengthened, and the per-salts can -be obtained in the wet way. - -Addition of hydrogen peroxide to a neutral or acid solution of a -titanium compound gives a yellow colour, due to the formation of a -peroxide, TiO₃,aq. Such solutions have the same oxidising powers as -hydrogen peroxide, but do not give the blue colouration with chromium -salts. By treatment of the solution with dilute alkalies, an hydrated -peroxide is thrown down, which, when dried over phosphoric anhydride, -has the formula TiO₃,3H₂O, and forms a yellow, horny mass. The freshly -precipitated peroxide dissolves in acids and alkalies; from the latter -solutions, by addition of hydrogen peroxide and alcohol, pertitanates of -various composition can be obtained, of which the following are -examples : Na₂O₂,TiO₃,3H₂O; (NH₄)₂O₂,TiO₃,H₂O₂; BaO₂,TiO₃,5H₂O; -K₂O₄,K₂O₂,TiO₃,10H₂O, etc. These salts lose hydrogen peroxide when -treated with dilute acids, and their constitutions are unknown. - -An interesting series of fluoroxypertitanates has been prepared by -oxidation of the solution of titanium dioxide in hydrofluoric acid with -hydrogen peroxide, and addition of metallic fluorides. The ammonium -compound, (NH₄)₃TiO₂F₅, crystallises in yellow octahedra, isomorphous -with the salts ZrF₄,3NH₄F and CbOF₃,3NH₄F. The potassium salt, K₂TiO₂F₄, -crystallises well from water, and is easily obtained in the pure state; -various barium salts are known. Similar compounds with oxalic acid have -also been prepared. - - -~Atomic Weight of Titanium.~--The first reliable determinations of this -constant were carried out by H. Rose in 1829. He determined the ratio -TiCl₄ : 4AgCl, by dissolving the pure tetrachloride, weighed in sealed -glass bulbs, in water in closed flasks, precipitating the dioxide by -ammonia, and weighing the silver chloride obtained by adding silver -nitrate to the filtered and acidified solution. He obtained the values -48·27 and 48·13, which agree very well with the accepted value, 48·1. In -the same year, Mosander, using a method not specified, obtained the -value 47·15. Determinations carried out by Pierre (1847) and Demoly -(1849) led to widely varying results. A series of determinations carried -out by Thorpe during the years 1883-1885 gave consistent results. The -method used was the precipitation of silver halide from the -tetrachloride and tetrabromide, and the mean value of seven series of -determinations gave the number 48·08. The International Committee have -adopted this result as the basis of the accepted value, 48·1. - - - ~Detection.~--The specific reactions for the element are frequently - masked by the presence of other metals, especially of iron, columbium, - tantalum, and vanadium, which most frequently accompany it in nature, - and from which a quantitative separation is frequently very difficult - (see p. 338). The most characteristic reactions are the following: - - (1) Reduction in acid solution by means of tin or zinc gives an - intense violet colour, due to the formation of trivalent titanium - salts. Various colours are given by vanadium, columbium, and tungsten, - so that the test is not decisive if these are present. - - (2) Hydrogen peroxide in acid solution gives a reddish-yellow colour, - which is very delicate, and is used in quantitative estimation; - vanadium compounds interfere. - - (3) In sulphuric acid solution, characteristic colours are obtained - with many phenolic compounds; thymol gives a blood-red colour which is - exceedingly intense. - - (4) A very characteristic and intense colour is given in acid solution - on the addition of 1:8-dihydroxynaphthalene-2:4-disulphonic acid - (chromotropic acid). - -The methods for the estimation of titanium are given in Chapter XXII. - - -CHAPTER XVI - -THE GROUP IVA ELEMENTS (_continued_)--ZIRCONIUM AND THORIUM - - -~Zirconium~, Zr = 90·6 - -The oxide zirconia was isolated as a new earth from zircon from Ceylon -by Klaproth in 1789; six years later the new earth was obtained also -from hyacinth, the gem-variety of the same mineral. The new oxide was -examined in 1818 by Berzelius, who pointed out its resemblance to -alumina, and gave it the formula Zr₂O₃; during the next two decades he -thoroughly investigated its properties, preparing the element itself, -and determining its equivalent. In 1857 a determination of the vapour -density of the chloride, by Deville and Troost, showed that the element -is really tetravalent, and that the formula ZrO₂ must be assigned to the -oxide; this formula was shown to accord with the isomorphism of rutile -(TiO₂) and zircon (ZrO₂,SiO₂) by Rose in 1859, whilst in the following -year Marignac observed the isomorphism between the fluozirconates of -zinc and nickel and the fluosilicates, fluotitanates, and fluostannates -of these metals. The homogeneity of the oxide has been questioned; -Svanberg in 1845 considered it to be a mixture of at least three earths, -whilst Sorby and Forbes in 1869 claimed to have discovered in it a new -oxide, ‘Jargonia.’ These claims, however, have been shown to have been -founded on inaccurate experimental work, and the individuality of the -element is at the present time considered to be well established. - -Zirconium is fairly widely distributed in nature, but generally in very -small quantities, and can be rightly classed as one of the rarer -elements. It occurs in some silicates, and in small quantities in almost -all the rare earth minerals. The most important source of the element -and its compounds was until quite recently the mineral Zircon, with its -gem-varieties Hyacinth and Jargon, and the large number of secondary -altered zircon minerals. Since its discovery in 1892, however, the -naturally occurring oxide, Baddeleyite,[455] has become increasingly -important for the extraction of zirconium compounds, especially for the -preparation of the pure oxide for fire-resistant materials. - - [455] For accounts of the zircon minerals, see pp. 47 and 75, and the - alphabetical list. - -The minerals may be treated by any of the usual methods. Zircon may be -fused with alkali or alkali carbonate; the cooled melt is extracted with -water, and the insoluble alkali zirconate decomposed by dilute acids; -from the solution, zirconia is thrown down by alkalies. Potassium -hydrogen fluoride and potassium hydrogen sulphate may be used for the -treatment either of zircon or of baddeleyite; in the first case, the -potassium fluozirconate formed may be dissolved by boiling with dilute -hydrofluoric acid, and separates out readily on cooling, whilst the -fluosilicate formed is not dissolved; the second treatment yields the -sulphate, which may also be dissolved out by dilute acid. A very -convenient method consists in reducing with carbon, either alone or in -presence of lime, at the temperature of the electric arc; the infusible -zirconium carbide is formed, whilst silica, if present, is reduced to -the carbide, which is volatile at that temperature and is therefore -driven off. The zirconium carbide may be dissolved in warm aqua regia. - -In all these methods the compounds obtained are contaminated with iron, -which clings to zirconium very tenaciously. Many methods have been -devised for its removal. A very suitable method is the thiosulphate -precipitation. Zirconia is thrown down quantitatively, mixed with -sulphur, from a not too strongly acid solution by addition of sodium -thiosulphate at the boiling-point, sulphur dioxide being at the same -time evolved, by decomposition of the potential thiosulphuric acid -formed by hydrolysis. Thorium and titanium accompany the zirconium, but -iron, aluminium, and the rare earths remain in solution. Another method -depends on the fact that zirconium is not precipitated from alkaline -solution by ammonium sulphide in the presence of tartaric acid, whereas -this reagent does not inhibit the precipitation of ferrous sulphide. -Iron may also be removed from a solution in concentrated hydrochloric -acid by means of ether, in which medium ferric chloride is easily -soluble. Zirconium compounds may be obtained free from iron by repeated -crystallisations of the oxychloride. - -Zirconium forms only one series of compounds, in which the metal is -tetravalent. Its chemical behaviour accords well with its position in -the periodic classification. It is somewhat more electropositive than -titanium, as shown by the fact that the hydroxide will not dissolve in -alkalies, though zirconates may be obtained by the fusion methods; the -oxide, however, is still a weak base, and the salts are to a large -extent hydrolysed in solution. The formation of a stable oxychloride, -which can be recrystallised without change in composition, shows clearly -the strengthening of the electropositive character. It has still, -however, in a high degree, the property of forming complex salts, which -is characteristic of the less electropositive metals. - -The group relations are borne out by the isomorphism of many related -salts. The hydroxide and oxide show polymeric modifications, and the -former has the usual tendency of compounds of this group to form -colloidal solutions, a tendency which extends to the element itself. The -metal resembles titanium in the eagerness with which it combines with -other elements, especially with oxygen, nitrogen, and carbon, whilst the -chloride closely resembles titanium tetrachloride in general properties, -and in the ease with which it forms addition and condensation products -with other substances. - -_The Metal._--All the difficulties which attend the attempts to prepare -metallic titanium in the pure state have to be encountered in the -preparation of metallic zirconium. The attempts which have been made -have used the same methods, and obtained much the same kind of result as -those employed in the case of titanium.[456] The reduction of potassium -fluozirconate by metallic potassium, first employed by Berzelius, gives -an amorphous product of unknown metal-content; it certainly contains a -considerable percentage of oxygen. The monoxide is obtained when -zirconia is reduced by magnesium (Winkler’s method). The reduction of -the fluozirconates of potassium by means of sodium gives better results -if the reaction is carried out in presence of sodium chloride in a -sealed iron bomb; the product after careful washing contains 97-98 per -cent. of the metal. Reduction with aluminium leads to the formation of -alloys; Weiss and Neumann[457] have used these in the form of pencils as -electrodes between which they pass the electric arc _in vacuo_, and so -obtain an almost pure zirconium. The 97-98 per cent. amorphous product -obtained by the sodium reduction also yields the practically pure metal -when treated in this way (compare Titanium, p. 223). A very pure -zirconium has been obtained by Wedekind[458] by heating the oxide with -fine calcium turnings in an evacuated iron tube; the powdered product is -washed, in absence of air, and heated in an evacuated porcelain tube to -800°-1000°, at which temperature the powder sinters into lumps which -take a brilliant polish and contain 99·1 per cent. of the metal. -Attempts to prepare a purer product from this by the method of Weiss and -Neumann were unsuccessful. - - [456] For a detailed account of these, see Lewis, _Studien über das - elementare Zirconium_, Stuttgart, 1912. - - [457] _Zeitsch. anorg. Chem._ 1909, ~65~, 248. - - [458] _Annalen_, 1913, ~395~, 149. - -The amorphous metal is a dark powder, which when washed with water on -the filter paper passes through as a dark blue colloidal solution; it -burns readily when heated in the air. According to Wedekind and -Lewis,[459] amorphous zirconium is really the colloidal form of the -metal. The fused metal is very hard (7-8, Mohs’ scale--it scratches -quartz but not topaz) and very brittle; it has the density 6·4, and is -of a whitish colour, with good metallic lustre on freshly broken -surfaces. The atomic heat is abnormally high, being approximately 7·3; -the element is paramagnetic. The melting-point was given by Wedekind -and Lewis[460] as 2330°-2380°, but later work of the former author[461] -gives the much lower value of 1530°, which seems more probable in view -of the fact that the element cannot be employed for electric lamp -filaments (see p. 322). - - [459] _Ibid._ 1910, ~371~, 367. - - [460] Weiss and Neumann, _loc. cit._; also Wedekind, _loc. cit._ - - [461] _Annalen_, 1913, ~395~, 149. - -Metallic zirconium is highly resistant to acids; it is attacked only by -hydrofluoric acid and by aqua regia. In the compact form it burns in the -air only at very high temperatures, though when powdered it glows in the -air at a red heat, forming probably a mixture of lower oxides. It is -attacked by chlorine and by hydrogen chloride at a red heat, with -formation of the chloride; fused potash also oxidises it, with evolution -of hydrogen. When heated in a current of hydrogen at a red heat, it -forms the _hydride_, ZrH₂,[462] as a velvet-black powder, which burns -with an intense bluish flame in oxygen, forming the sesquioxide, Zr₂O₃. -When heated in nitrogen or ammonia, amorphous zirconium yields -_nitrides_, which are also obtained when any attempt is made to reduce -zirconium compounds to the metal in air. The most definite is the -compound Zr₂N₃,[462] which forms a bronze-coloured powder, resistant to -all mineral acids except hydrofluoric acid. Chlorine and bromine -transform this to the halide. - - [462] Wedekind and Lewis, _Annalen_, 1910, ~371~, 367. - -The _hydroxide_ is of doubtful individuality, since on drying it loses -water progressively as the temperature is raised, no definite stable -compound being known; in this respect zirconium resembles titanium. When -heated to 100°, its composition corresponds approximately with that -required by the formula ZrO₂,H₂O, but the percentage of water varies -with the history of the specimen. When precipitated by alkalies in the -cold, it forms the so-called α or ortho modification, which, like the -analogous titanium compound, is readily soluble in dilute acids, and -glows when heated. By precipitation at the boiling point, the β form is -obtained; this is less soluble in acids, and does not glow when heated. -The differences between the two forms are by no means sharply marked; -they are rather the limiting forms of a continuously varying series than -distinct chemical individuals, and the properties of any hydroxide -precipitate depend very largely on the conditions under which it is -thrown down. - -The hydroxide is insoluble in water, but can be obtained in colloidal -solution after it has been repeatedly heated with dilute acids, which -serve to break down the molecular complexes; it can be also readily -obtained in colloidal solution by dialysis of the nitrate, chloride, or -acetate. In these solutions it is positively charged; electrolytes -precipitate it with great ease. The gel has a very high power of forming -adsorption products. When thrown down from solution by soda or potash, -it carries down considerable quantities of alkali, to which it clings so -tenaciously that the most careful washing cannot entirely remove them. -If the gel be placed in contact with an ammoniacal solution of a cupric -compound, it removes the cuprammonium complex entirely from the -solution, becoming itself deep blue in colour, and leaving the liquid -quite clear and colourless. In colloidal solution it forms adsorption -compounds with negatively charged colloids, especially metals, the gels -obtained from such solutions containing both colloids. - -In the presence of hydrogen peroxide, ammonia throws down an hydrated -peroxide, which is also obtained[463] by electrolysis of a brine -solution in which the hydroxide is suspended, oxidation being effected -by the sodium hypochlorite formed. This reaction is expressed by the -equation: - - Zr(OH)₄ + NaOCl = Zr(OOH)(OH)₃ + NaCl - - [463] Pissarjewski, _Zeitsch. anorg. Chem._ 1900, ~25~, 378. - -It is an endothermic compound, and is very unstable, losing oxygen on -standing; by the action of acids it gives hydrogen peroxide. It -dissolves in alkalies containing hydrogen peroxide; from such solutions, -alcohol precipitates salts of the formula R´₄Zr₂O₁₁,9H₂O. - -_Zirconium oxide_, ZrO₂, occurs in nature; it can be obtained in the -laboratory as a voluminous white powder by ignition of the hydroxide or -a suitable salt. The physical properties are described under the mineral -Baddeleyite (p. 75) and in Chapter XXI (p. 323), in which an account of -its technical applications is given. The melting-point is probably -about 2700°; at 3000° it begins to volatilise. It dissolves readily in -mineral acids, unless previously ignited very strongly; all specimens -dissolve easily in hydrofluoric acid, and are readily converted by -concentrated sulphuric acid into the sulphate. - -When fused with metallic oxides or carbonates, it gives crystalline -_zirconates_, of which a large number have been prepared; the calcium -compound, CaZrO₃, is said to be isomorphous with perovskite, CaTiO₃. - -A _suboxide_, ZrO, of somewhat doubtful individuality,[464] is said to -be obtained when the dioxide is reduced with magnesium; it forms a dry -black powder, which is not attacked by acids, and when heated glows, -forming the dioxide. A _sesquioxide_, Zr₂O₃, is obtained as a greenish -powder when the hydride is burnt in oxygen; when heated in the air, it -oxidises very slowly, forming the dioxide. - - [464] Wedekind and Teletow (_Annalen_, 1913, ~395~, 149) have recently - denied the existence of this oxide. - -An _oxysulphide_, ZrOS, is obtained when the anhydrous sulphate is -heated in a current of sulphuretted hydrogen; it is a bright yellow -powder, which ignites spontaneously in the air. No disulphide is known. -The _carbide_, ZrC, is obtained, according to Moissan and Lengfeld,[465] -when the oxide is heated with carbon in any proportions, excess of -carbon separating on cooling as graphite; the process is hastened by -addition of lime. It is a hard, dark-grey solid, and is a very good -conductor of electricity. When heated in oxygen or nitrogen, it reacts -readily, forming the oxide and nitride respectively; halogens attack it -at quite low temperatures (250°-400°), forming the halide compounds, -which are indeed best prepared in this way. Strong mineral acids, with -the exception of hydrochloric acid, attack it, and fused alkalies -dissolve it readily. - - [465] _Compt. rend._ 1896, ~122~, 651. - -The _fluoride_, ZrF₄, is best obtained by the action of anhydrous -hydrofluoric acid on the chloride. It forms a white crystalline mass, -which readily sublimes, and is soluble in hydrofluoric acid; from the -solution it crystallises as the trihydrate, ZrF₄,3H₂O. The anhydrous -substance is very slightly soluble in water in the cold; when warmed, it -hydrolyses, forming the hydroxide. The solution in hydrofluoric acid -dissolves metallic carbonates and oxides, forming the numerous -_fluozirconates_ or _zirconofluorides_. - -There are many types of these compounds, of which the potassium salt, -K₂ZrF₆, is the most important. The solubility of this salt increases -very rapidly with the temperature; 100 parts of water dissolve, at 15°, -1·41 parts, at 100°, 25 parts of the compound. It has been frequently -used for the purification of zirconium compounds, for the preparation of -the element, and for analytical determinations. Other potassium salts, -K₃ZrF₇ and KZrF₅,H₂O, are obtained by using a large excess of potassium -fluoride and zirconium fluoride respectively. The ammonium compounds are -analogous in composition to the potassium salts, but the sodium salt, -Na₅ZrF₉, is obtained from mixtures of the components in all proportions; -on account of its very low solubility, it can be obtained by double -decomposition of the potassium salt with sodium chloride. Of the salts -with divalent metals, the types R´´ZrF₆,_x_H₂O and R´´₂ZrF₈,_x_H₂O, are -the most common. - -The _chloride_, ZrCl₄, is known, on account of the ease with which it -hydrolyses, in the anhydrous state only. It can be obtained by all the -usual methods, of which perhaps the action of chlorine on the carbide, -and of carbon tetrachloride, or a mixture of chlorine and sulphur -monochloride, on the oxide, are the most convenient; an interesting -method consists in heating the oxide with phosphorus pentachloride in a -closed tube at 190°. It forms a volatile white sublimate, which fumes -strongly in air, and reacts vigorously with water; it is soluble in -ether. It forms a series of addition compounds with ammonia and organic -bases, as well as with the chlorides of non-metallic elements; warmed -with phosphorus pentachloride, it forms a stable solid, 2ZrCl₄,PCl₅, -which melts at 240°, and boils at 345°. With organic compounds, -especially with esters, acids, and phenols, it forms a long series of -addition and condensation products, of which the compounds -ZrCl₄(C₆H₅·COOC₂H₅)₂ and ZrCl₂[O·C₆H₅·CHO]₂ may be taken as examples. -By addition of organic bases to a solution of the chloride in alcoholic -hydrogen chloride, double chlorides of the type (C₅H₅NH)₂ZrCl₆ are -obtained. - -The _oxychloride_, ZrOCl₂,8H₂O, separates in characteristic tetragonal -prisms when the tetrachloride is dissolved in water or hydrochloric acid -of any concentration. It is readily soluble in water and alcohol, but -sparingly soluble in hydrochloric acid, from which therefore it is -generally recrystallised. According to Chauvenet,[466] it effloresces in -dry air, forming the hexahydrate, ZrOCl₂,6H₂O; when dried in a vacuum, -it forms the hydrate, ZrOCl₂,3¹⁄₂H₂O, whilst the dihydrate, ZrOCl₂,2H₂O, -is obtained by heating at 100°-105° in hydrogen chloride. When the -dihydrate is heated to 230°, it forms another basic chloride, -ZrOCl₂ZrO₂,[467] which is stable up to 600°; above this temperature, it -breaks up, forming the volatile tetrachloride, and leaving a residue of -the dioxide. - - [466] _Compt. rend._ 1912, ~154~, 821. - - [467] _Ibid._ 1234. - -By repeated evaporation of the oxychloride with small quantities of -water, a ‘metazirconium chloride’ is obtained, which dissolves in water -to a colloidal solution, and on dialysis yields a colloidal solution of -‘metazirconic acid.’ - -The _bromide_, ZrBr₄, very closely resembles the chloride; when treated -with water it forms the oxybromide, which separates from solution -according to the conditions in various hydrated forms, of which the -commonest is the octohydrate, ZrOBr₂,8H₂O. The _iodide_, ZrI₄, is a very -reactive body, which closely resembles the preceding; it forms an -oxyiodide, ZrOI₂,8H₂O. - -_Zirconyl chlorate_, ZrO(ClO₃)₂,6H₂O, is obtained from the sulphate by -double decomposition with barium chlorate; it forms very soluble -colourless needles. Alkali iodates or iodic acid throw down a voluminous -_oxyiodate_, very sparingly soluble, like the corresponding ceric and -thorium salts, in water and acids. - -_The Sulphates._--When zirconium dioxide is dissolved in concentrated -sulphuric acid, and the excess of acid removed by heating to 400°, the -‘neutral’ sulphate, Zr(SO₄)₂, remains. The compound dissolves in dilute -sulphuric acid to form solutions which contain various ‘complexes’ as -shown by conductivity measurements, and the behaviour towards oxalic -acid. Whilst solutions of the nitrate or chloride give immediate -precipitates with this reagent, solutions of the ‘sulphate’ give no -precipitate, or at most a very gradual one; moreover, addition of -sulphuric acid or of alkali sulphates to other zirconium salts inhibits -the oxalate precipitation. These facts are explained by regarding the -‘neutral’ sulphate, Zr(SO₄)₂,4H₂O, as zirconylsulphuric acid, -ZrOSO₄,H₂SO₄,3H₂O, which in solution ionises to 2H^{.} and ZrOSO₄,SO₄´´. -This conclusion is confirmed by the fact that whilst in solutions of the -chloride in hydrochloric acid, zirconium goes on electrolysis to the -cathode, on addition of sulphuric acid to the solution it travels to the -anode. The anhydrous compound and the hydrate are extremely soluble in -water, but much less readily soluble in dilute sulphuric acid. Probably -in solution more complex salts are formed by further hydrolysis, for by -addition of concentrated alkali sulphate solution in the cold, double -salts of the formula Zr₂O₃(RSO₄)₂,8H₂O are obtained. When the solution -is kept for some time at 39°-40°, a basic sulphate, 4ZrO₂,3SO₃,14H₂O, -separates slowly. When concentrated solutions are boiled, a salt, -2ZrO₂,3SO₃,5H₂O, separates as a crystalline precipitate; in contact with -water it slowly hydrates itself to the compound 2ZrO₂,3SO₃,14H₂O; when -heated to 300°, it becomes anhydrous without further change. Various -other basic, acid and complex salts have also been described. - -The _nitrate_, Zr(NO₃)₄,5H₂O, separates from concentrated solutions -of the oxide in nitric acid by evaporation over sulphuric acid -and sodium hydroxide; it is believed to be a zirconylnitric acid, -ZrO(NO₃)₂,2HNO₃,4H₂O by analogy with the sulphate. When its aqueous -solutions are warmed, basic salts separate. Kolbe[468] has described an -additive compound with antipyrine, Zr(NO₃)₄,6C₁₁H₁₂ON₂, which is soluble -in water, and melts at 217°-218°. - - [468] _Zeitsch. anorg. Chem._ 1913, ~83~, 143. - -When phosphoric acid or a soluble phosphate is added to a solution of a -zirconium salt, _zirconium phosphates_ of doubtful composition are -thrown down; by fusion methods, various double phosphates have been -prepared. A _hypophosphate_, Zr(PO₃)₂,H₂O, has recently been obtained -by Hauser and Herzfeld[469] by precipitation. The same authors have -prepared a _hypophosphite_, which is sensitive to light. When -hypophosphorous acid, H₃PO₂, is added to a solution of zirconium -nitrate, a precipitate is obtained, which dissolves in excess of the -acid; by addition of alcohol to the clear solution, the hypophosphite, -Zr(H₂PO₂)₄,H₂O, is thrown down in colourless, highly refracting prisms, -which on exposure to sunlight for a short time become deep violet, -without further perceptible change. - - [469] _Zeitsch. anorg. Chem._ 1913, ~84~, 92. - -_Zirconium carbonate_ has recently been obtained by Chauvenet.[470] -Addition of sodium carbonate precipitates a basic orthocarbonate, -ZrCO₄,ZrO₂,8H₂O, soluble in excess; when dried in vacuo, the precipitate -loses water, forming the dihydrate, ZrCO₄,ZrO₂,2H₂O. When the latter -compound is treated with carbon dioxide at a pressure of 30-40 -atmospheres, the neutral orthocarbonate, ZrCO₄,2H₂O, is formed. When the -compounds are heated, other basic salts are obtained. - - [470] _Bull. Soc. Chim._ 1913 [iv.], ~13~, 454. - -_Zirconyl oxalate_, ZrO,C₂O₄, is obtained in the hydrated form when -oxalic acid is added to a zirconium salt in the presence of hydrochloric -or acetic acid. It is a white powder, soluble in oxalic acid, and easily -hydrolysed by water. If an aqueous solution of oxalic acid be saturated -with zirconium hydroxide, an acid oxalate, ZrOH(HC₂O₄)₃,7H₂O, is -obtained on evaporation. Double oxalates are readily obtained by -dissolving zirconium hydroxide in solutions of alkali hydrogen oxalates, -the general form being Zr(C₂O₄R´)₄,xH₂O. The _tartrate_ precipitated -when tartaric acid is added to a zirconium salt in solution probably has -the cyclic structure, - - COOZr(OH)₃ - | - CH--O - | \ - | Zr(OH)₂ - | / - CH--O - | - COOZr(OH)₃ - -as shown by the great rise in the specific rotatory power of solutions -of alkali oxalates on addition of zirconium compounds. The precipitate -dissolves readily in alkalies, and various double alkali tartrates have -been prepared; the potassium salt, ZrO(C₄H₄O₆K)₂,3H₂O, is analogous to -the thorium alkali tartrates. The solubility in alkalies is of great -importance for the separation of iron and zirconium. - - -~Atomic Weight of Zirconium.~--The value of this constant is not very -accurately known. The International Committee has adopted the value -90·6, but there is some uncertainty as to the value of the decimal -fraction. Berzelius in 1825 employed the analytical sulphate method, and -found Zr = 88·47. The numbers of Hermann (1844), obtained by the -analysis of the oxychloride, 2ZrOCl₂,9H₂O,[471] were very discordant, -the mean giving the value 89·56. Marignac in 1860 analysed the potassium -salt, K₂ZrF₆; this he heated with strong sulphuric acid, the residue -being ignited until all the zirconium sulphate was transformed to oxide; -the weighed mixture was then freed from potassium sulphate, and the -residual oxide dried and weighed. From the three ratios K₂ZrF₆ : ZrO₂, -K₂ZrF₆ : H₂SO₄, and K₂SO₄ : ZrO₂, he obtained the mean values 90·02, -91·55, and 90·68 respectively. Weibull in 1881-1882 determined the -ratios Zr(SO₄)₂ : ZrO₂ and Zr(SeO₄)₂ : ZrO₂ by ignition of the sulphate -and selenate respectively; he obtained the values 89·55 and 90·81. - - [471] Chauvenet (_loc. cit._) could not confirm the existence of this - hydrate. - -Bailey carried out a series of analytical sulphate determinations in -1890, obtaining the mean value 90·656. Brauner criticises the method on -the ground that the preparation of the pure neutral anhydrous sulphate -is almost impossible; the sulphate heated to 400° is not yet anhydrous, -so that Bailey’s result, on this ground, is probably too low. Venable in -1898 analysed the oxychloride; he claimed to have obtained the compound -ZrOCl₂,3H₂O, by heating the crystallised salt at 100°-125° in hydrogen -chloride, a method which Chauvenet (_loc. cit._) has found to lead to -the dihydrate, ZrOCl₂,2H₂O. His value was 90·803. - - -~Detection and Estimation.~--The following reactions may be employed to -distinguish zirconium: - -(1) The oxalate precipitated from neutral or faintly acid solution -dissolves readily in excess of oxalic acid; the oxalates of thorium and -of the rare earth elements are practically insoluble under these -conditions. The fluoride also dissolves in excess of hydrofluoric acid -or of alkali fluoride, behaviour characteristic of this element alone -among the group. - -(2) By fusion with sodium carbonate in the oxidising flame, a bead is -obtained, which, when dissolved in boiling hydrochloric acid, forms a -solution which gives a voluminous precipitate on addition of disodium -hydrogen phosphate, if zirconium is present. Iron, aluminium, titanium, -thorium, and rare earths have no influence on the test.[472] - - [472] Biltz and Mecklenburg, _Zeitsch. angew. Chem._ 1912, ~25~, 2110. - -(3) A solution of a zirconium salt in hydrochloric acid gives an orange -colouration with curcuma paper. Ferric and titanium salts, if present, -must be reduced by means of zinc before the test is applied. - -The _estimation_ of zirconium is complicated by the difficulty of -separating it from the accompanying elements. The solubility of the -oxalate in oxalic acid allows of a rapid and easy separation from -thorium and rare earth elements, so that iron, aluminium, and chromium -only remain to be removed. Iron may be separated by the thiosulphate -method, or other processes mentioned on p. 338; when free from that -element, zirconium may be separated from aluminium and chromium by -precipitation with alkali iodate in presence of the least possible -excess of acid. The precipitates in the thiosulphate and iodate methods -may be washed, and ignited directly to the dioxide, which is weighed as -such; if the zirconium is left after separation in solution, it may be -precipitated with ammonia,[473] and after washing and drying, ignited -and weighed as dioxide. - - [473] On account of the adsorption of alkalies by the zirconium oxide - gel, potash or soda is never used for this precipitation. - - -~Thorium~, Th = 232·4 - -The name Thoria (thorina) was proposed by Berzelius in 1817 for what -appeared to be a new earth, but which in 1824 was recognised as a basic -yttria phosphate. In 1828 a new mineral was discovered by Esmark near -Brevig in Norway; to the oxide isolated from this, Berzelius gave the -name thoria, from its resemblance to the substance he had obtained in -1817. The homogeneity of the new element was questioned by Bergmann in -1857, and also by Bahr in 1862, but the conclusions of those authors -have been shown to be quite unfounded. - -Thorium occurs in traces in a large number of common minerals, and in -varying quantities in most of the uranium and rare earth minerals. Its -occurrence in monazite, and the distribution of the latter mineral, have -already been dealt with; the commercial treatment of monazite is -described in Chapter XVIII. The oxide forms the chief constituent in -Thorite, with its gem-variety Orangite, and the various secondary -minerals, and in the mineral Thorianite, in which the only other -important constituent is uranous oxide. The extraction from these -minerals is a comparatively simple matter. Decomposition is easily -effected by hydrochloric or sulphuric acid, thorianite dissolving easily -also in nitric acid; the solutions obtained, after appropriate treatment -to remove silica, excess of acid, etc., are treated with sulphuretted -hydrogen, to remove lead, bismuth, and similar foreign metals, and freed -from the rare earths by the carbonate, oxalate, or sulphate methods. The -last depends on the fact that thorium sulphate and its hydrates are much -less soluble than corresponding compounds of the rare earth elements; -the first two on the fact that thorium salts dissolve readily in excess -of alkali carbonates or oxalates, whilst the rare earth compounds are -much less easily soluble. - -Thorium, like zirconium, forms only one series of salts, in which the -metal is tetravalent. The formula ThO was originally put forward by -Berzelius for the oxide, from its resemblance to the ceria and yttria -oxides, and its general occurrence with these. The true formula was -deduced, when the valency of zirconium had been decided by the vapour -density experiments of Troost and Deville, in 1857, from the isomorphism -of zircon and thorite, and the close relationship between the compounds -of the two elements, especially among the double fluorides, and was -confirmed by a determination of the specific heat of the metal by Nilson -in 1883. - -In its chemical relations, the element resembles zirconium, though, as -is to be expected from the high atomic weight, it shows a much more -marked electropositive character, approaching in this respect the -elements of the yttrium group. The oxide has no longer acid properties, -and the neutral salts, though they hydrolyse readily and are therefore -acid to indicators in solution, may be recrystallised unchanged from -aqueous solution. The tendency to form double salts is still present, -though diminished; the oxalate is soluble in a large excess of alkali -oxalate, but not in oxalic acid, and the double fluorides are less -numerous and varied than those of zirconium and titanium. On the other -hand, it forms a well-crystallised and characteristic series of double -nitrates, R´₂Th(NO₃)₆, isomorphous with the analogous ceric salts. In -the behaviour of its sulphate it differs markedly from zirconium, and -closely approaches the rare earth elements. The hydroxide has the -characteristic tendency to form colloidal solutions and gels. - -Thorium is peculiar, among the elements which have been considered, -through its property of giving characteristic radiations, and -disintegrating with formation of a whole family of new elements; or, as -it is commonly expressed, through its radioactive properties.[474] The -element has a half-life period of the order of 4 × 10¹⁰ years; in the -course of decay, it gives rise to mesothorium 1, which is rayless, but -decays to mesothorium 2, with its product radiothorium, both of which -give powerful radiations. Mesothorium 1 of course occurs in all -thorium-containing minerals, and may be separated from monazite by -addition of a barium compound during the sulphuric acid decomposition; -in consequence of the powerful radiating properties of its products, it -is itself of considerable importance, and proposals for extracting it -from monazite in the preparation of the thorium nitrate of commerce have -been put forward (see p. 276). - - [474] The nature of the present work allows only the briefest - reference to be made to the exceedingly interesting phenomena which - centre about this subject; for a more complete account, the student - should consult Soddy, _The Chemistry of the Radio-Elements_, Part I, - 1911. - -Mesothorium appears to be chemically identical with radium; since -monazite, like all other thorium-bearing minerals, contains uranium and -radium, the latter element is separated with the mesothorium, and -indeed, having a very much larger half-life period, constitutes by far -the greater part of such ‘mesothorium’ preparations. On account of the -great activity of the mesothorium products, the best preparations from -monazite, though estimated to contain only 1 per cent. of mesothorium to -99 per cent. radium, are said to be four times as active as pure radium -compounds. The chemical identity of the two products seems to preclude -any possibility of determining the physical properties and constants of -mesothorium. - -The element radiothorium, which was discovered by Hahn in 1905, in the -mineral thorianite, is chemically identical with the parent element -thorium, but can be separated by means of the intermediate element, -mesothorium 1. The latter is readily separated by the sulphate -precipitation, and the radiothorium to which it gives rise may be -separated by precipitation with ammonia. Thorium is also chemically -identical with ionium, the parent of radium, and the thorium nitrate of -commerce therefore contains important quantities of ionium--important -that is, in view of the high radiating power of the latter element. The -study of these relationships constitutes one of the most important and -interesting fields in the province of radioactivity. - -_The Metal._--Elementary thorium has not yet been obtained in the pure -state, owing to the ease with which it forms compounds and alloys with -all the common elements, and to its great affinity for oxygen; the high -melting-point also increases the difficulty of obtaining the pure metal. -Berzelius attempted to reduce the alkali double fluorides and double -chlorides with sodium or potassium; Nilson carried out the same reaction -in a closed iron cylinder, but his product still contained 20 per cent. -of thoria. Reduction of the oxide with magnesium is never complete, and -the carbon method gives only a mixture of carbide and metal. -Electrolytic methods give no better results, since the metal liberated -at the cathode always encloses oxide and other impurities. Moissan and -Hönigschmid in 1906, by heating the carefully purified anhydrous -chloride with sodium in a sealed glass tube from which air and moisture -had been removed, claim to have obtained a product containing only 3 per -cent. of the oxide. The element has recently been prepared in leaf form -by forcing the amorphous product into the bore of a copper tube, -hammering into sheets, and removing the copper by dilute nitric -acid.[475] - - [475] v. Bolton, _Zeitsch. Elektrochem._ 1908, ~14~, 768. - -The amorphous impure metal is a dark grey powder, of specific gravity -11·3; the hammered and strongly heated leaf has the density 12·16. It -burns readily in air with great brilliance, and when finely powdered -ignites if crushed or rubbed. When heated in the electric furnace, it -melts, according to von Bolton,[476] at about 1450°; von Wartenburg[477] -found the melting-point to be about 1700°; the fused beads resemble -platinum in physical properties. It is somewhat resistant to acids, -dissolving easily only in aqua regia, and more slowly in fuming -hydrochloric acid. It combines directly when heated in sulphur or -halogens, and in nitrogen and hydrogen. - - [476] v. Bolton, _Zeitsch. Elektrochem._ 1908, ~14~, 768. - - [477] _Ibid._ 1909, ~15~, 866. - -The _hydride_, ThH₄, is best obtained by heating the metal in hydrogen, -an energetic reaction taking place at a red heat. Winkler observed that -a mixture of the dioxide with magnesium absorbs hydrogen readily when -heated. The hydride is a stable greyish-black powder, not attacked by -water, but dissolving readily in hydrochloric acid, with evolution of -hydrogen. The _nitride_, Th₃N₄, is prepared by heating the metal in the -gas, or the carbide in a stream of ammonia. It is a brown powder, -decomposed by water with evolution of ammonia and formation of the -dioxide. The _azide_ has been used for purposes of detection and -estimation, since in boiling solution it is hydrolysed with separation -of the hydroxide; zirconium and ceric salts also show this reaction, but -the rare earth salts give no precipitate. - -The _hydroxide_, Th(OH)₄,_x_H₂O, is precipitated from solutions of -thorium salts by alkalies or ammonia, as a gelatinous white precipitate, -insoluble in excess. It dissolves readily in mineral acids or in alkali -carbonates. Hydrogen peroxide and ammonia throw down an hydrated -_peroxide_, Th₂O₇; from neutral solutions hydrogen peroxide alone throws -down _peroxy-salts_, which contain acid groups. This peroxide may also -be obtained by the action of sodium hypochlorite or hydrogen peroxide on -the hydroxide, as in the case of the zirconium compound. It readily -gives up oxygen, passing into the more stable peroxide, ThO₃. Since in -neutral or faintly acid solutions zirconium and the rare earths give no -precipitate with hydrogen peroxide, the reaction is extremely useful in -the detection and estimation of thorium. - -_Thorium dioxide_, ThO₂, is obtained by the ignition of the hydroxide or -of suitable salts as a white powder, of which the properties and -appearance depend largely on the method and temperature used in its -formation. Whilst the residue obtained by ignition of the nitrate is an -extraordinarily voluminous and light flaky mass, the sulphate yields a -dense thick powder; the nitrate was therefore always preferred in the -manufacture of incandescent mantles (_q.v._), as it was thought that the -oxide obtained from it was the most suitable for illumination. In the -crystalline form the oxide has been obtained in the laboratory by fusion -with borax and with potassium phosphate. The first method gives -tetragonal crystals, probably isomorphous with those of rutile and -cassiterite; the phosphate fusion is said to give cubic crystals (see p. -74). The oxide is insoluble in acids, but can be transformed into the -sulphate by evaporation with concentrated sulphuric acid, or fusion with -alkali bisulphate. It does not liberate carbon dioxide when fused with -alkali carbonates. - -By repeated evaporation with small quantities of acids, thoria can be -transformed into a gel soluble in water (thorium meta-oxide). The sol is -an opalescent fluid, orange-red by transmitted light, and contains small -quantities of the acid employed. The hydroxide may also be obtained in -this form by carefully washing it, and boiling with small quantities of -acids, or with thorium or other salts, or even by long continued washing -with pure water; similarly, continued dialysis of thorium salts -eventually yields such gels. The colloid is positively charged, and -resembles the zirconium oxide gel in its relation to negatively charged -colloids. The gel is easily precipitated by electrolytes. - -Ignited thorium oxide has found considerable application in recent years -a catalyst in the preparation of ketones by the contact method of -Sabatier and Senderens.[478] By passing mixtures of the vapours of -appropriate acids over the catalyst heated to the necessary temperature, -good yields of the required ketones are obtained.[479] - - [478] Cf. Senderens, _Ann. Chim. Phys._ 1913 [viii.], ~28~, 143. - - [479] Cf. Pickard and Kenyon, _Trans. Chem. Soc._ 1913, ~103~, 1923. - -The _sulphide_, ThS₂, is obtained, together with the oxysulphide, ThOS, -according to Duboin,[480] by passing a current of sulphuretted hydrogen -over a mixture of thorium chloride with excess of sodium chloride, at a -red heat. The former forms large brown crystals, from which the small -orange-yellow crystals of the oxysulphide may be separated by means of a -sieve; the latter is purified by treatment with warm nitric acid, which -dissolves the sulphide very readily. The oxysulphide is also obtained -when the anhydrous sulphate is heated in sulphuretted hydrogen.[481] - - [480] _Compt. rend._ 1908, ~146~, 815. - - [481] Hauser, _Zeitsch. anorg. Chem._ 1907, ~53~, 74. - -The _carbide_, ThC₂, is obtained by the action of carbon on the oxide in -the electric furnace; it is a yellow crystalline mass, decomposed slowly -by water, energetically by dilute acids in the cold, with evolution of a -complex mixture of hydrogen and hydrocarbons, in which many members of -the paraffin, olefine and acetylene series have been observed.[482] -Hydrogen constitutes over 50 per cent. of the mixture, the next most -important constituents being the acetylenic hydrocarbons, followed by -ethane. - - [482] Lebeau and Damiens, _Compt. rend._ 1913, ~156~, 1987. - -_Thorium fluoride_, ThF₄, is obtained anhydrous by passing hydrogen -fluoride over the anhydrous chloride or bromide at a temperature of -350°-400°. The tetrahydrate, ThF₄,4H₂O, is precipitated by addition of -hydrofluoric acid to a solution of a thorium salt, or by the action of -the acid on the hydroxide. Hydrofluosilicic acid also throws down the -fluoride, even in the cold, from solutions of thorium salts. The -fluoride is insoluble in water and mineral acids, as well as in excess -of precipitant; this behaviour allows of a complete and easy separation -of thorium from titanium and zirconium. The rare earth fluorides are -also much more easily soluble in concentrated mineral acids than thorium -fluoride, so that this compound may also be used in the separation from -the rare earths. When heated in a stream of the acid to 800°, the -hydrated salt yields the oxyfluoride, ThOF₂; ignited in the air, it -leaves the dioxide. Precipitation with potassium fluoride gives the -_double fluoride_, KThF₅,H₂O, which may be obtained anhydrous by fusion -of the mixed fluorides; it is insoluble. An amorphous insoluble -compound, K₂ThF₆,4H₂O, is obtained by boiling the hydroxide with a -mixture of potassium hydrogen fluoride and hydrofluoric acid. Sodium and -ammonium fluorides throw down the simple fluoride. - -_Thorium chloride_, ThCl₄, is obtained in the anhydrous form by all the -usual methods, the most convenient being perhaps the action of chlorine -and sulphur monochloride on the heated dioxide. It almost invariably -contains small quantities of oxychloride. When pure, it forms colourless -needles fairly stable in dry air; the impure product gradually darkens -in colour. It dissolves in water with considerable evolution of heat, -and is soluble also in alcohol and moist ether. It melts at about 820°, -and sublimes unchanged at somewhat higher temperatures; the vapour -begins to dissociate at about 1050°, the dissociation increasing rapidly -as the temperature rises. It resembles zirconium chloride in the ease -with which it forms additive compounds with ammonia and organic bases, -and addition and condensation products with organic oxygen-compounds; -many _double_ and _complex chlorides_ are also known, among which the -platinum compounds ThPtCl₈,12H₂O and Th₂Pt₃Cl₁₄,24H₂O, and the pyridine -salt (C₅H₅NH)₂ThCl₆ may be mentioned. - -From aqueous solution the octohydrate, ThCl₄,8H₂O, separates at ordinary -temperatures; a heptahydrate and an enneahydrate have been described as -precipitated from the alcoholic solution by addition of water. The -_basic salts_, Th(OH)Cl₃,7H₂O and Th(OH)₂Cl₂,5H₂O, have been obtained -by addition of the hydroxide to alcoholic hydrogen chloride. The -_oxychloride_, ThOCl₂, may be obtained by the carefully regulated action -of carbon tetrachloride on the dioxide, according to the equation: - - ThO₂ + CCl₄ = ThOCl₂ + COCl₂ - -It is a colourless crystalline solid, which takes up moisture from the -air, forming the hexahydrate. - -_Thorium bromide_, ThBr₄, is a volatile solid which boils at 725°; it -closely resembles the chloride. The _iodide_ and a _basic iodide_, -Th(OH)I₃,10H₂O, are known. - -No cyanide of thorium is known, addition of potassium cyanide merely -causing separation of the hydroxide. A _ferrocyanide_, Th[Fe(CN)₆],4H₂O, -is thrown down as a white powder by potassium ferrocyanide; with -potassium ferricyanide no precipitate is obtained. The _platinocyanide_, -Th[Pt(CN)₄]₂,16H₂O, is obtained by double decomposition in -yellowish-brown prisms. - -Among the halogen oxysalts, the _perchlorate_, _chlorate_, _bromate_, -and _iodate_ were prepared by Cleve. The iodate is of great importance -for purposes of detection and estimation, from the fact that, in -presence of a large excess of alkali iodate, it is insoluble in strong -nitric acid, whilst the analogous compounds of the rare earth elements -dissolve readily in that solvent. - -The _sulphate_, Th(SO₄)₂, is obtained anhydrous by evaporating the -excess of acid from a solution of the dioxide in oil of vitriol, or by -heating the hydrates. It resembles the sulphates of the rare earth -elements, in that it dissolves in water at 0° to form a highly -supersaturated solution, from which the hydrated forms separate out -almost quantitatively when the temperature is allowed to rise. The -solubility relations of the various hydrates, on account of their -commercial importance, are somewhat fully treated in Chapter XVIII. A -dihydrate, Th(SO₄)₂,2H₂O, is obtained by keeping the tetrahydrate at -110°. The ennea- and octohydrates are isomorphous with the corresponding -thorium selenate hydrates, and the ennea- and tetrahydrates with the -analogous uranous sulphate hydrates. The hydrates yield the anhydrous -salt when heated to 400°; the anhydrous sulphate has already a -considerable dissociation tension (15 mm.) at 575°. By treatment with -excess of acid, and subsequent heating to 130° _in vacuo_, the _acid -sulphate_, Th(SO₄),H₂SO₄, is obtained. An insoluble _basic salt_, -ThOSO₄,2H₂O, is formed by continued boiling of the tetrahydrate in -dilute solution, or more quickly by heating the solution in a closed -tube to 120°-125°; a monohydrate, ThOSO₄,H₂O, is also known. Halla[483] -has recently obtained the hydrate, ThOSO₄,5H₂O, by boiling a solution of -the neutral sulphate with magnesium sulphate, and also by treating the -anhydrous sulphate with a little water in presence of magnesium -carbonate. - - [483] _Zeitsch. anorg. Chem._ 1912, ~79~, 260. - -By precipitation with potassium sulphate the _double salt_, -Th(SO₄)₂,2K₂SO₄,2H₂O, is formed; this is soluble in water but insoluble -in potassium sulphate solution. The analogous sodium and ammonium salts -are soluble both in water and excess of the corresponding alkali -sulphate. - -The _sulphite_, Th(SO₃)₂,H₂O, is obtained as a white amorphous -precipitate by warming a solution of a thorium salt with sulphurous -acid. Basic sulphites and double sulphites are also known; the -precipitates obtained by addition of alkali sulphite dissolve readily in -excess. The hydroxide is almost insoluble in sulphurous acid, behaviour -which distinguishes thorium (and zirconium) from all the trivalent -metals. No _thiosulphate_ is known, the hydroxide being thrown down from -boiling solution by addition of sodium thiosulphate: this method of -precipitation was formerly much used for purposes of estimation, but it -is more tedious and less accurate than the modern methods. - -_Thorium nitrate_, Th(NO₃)₄,12H₂O, crystallises at ordinary temperatures -in large hygroscopic tablets, very soluble in water and alcohol. The -hydrates, Th(NO₃)₄,6H₂O and Th(NO₃)₄,5H₂O, have been obtained from hot -solution and from nitric acid solution respectively. Thorium is employed -in commerce almost entirely in the form of this salt, which is -dehydrated until it contains about 48 per cent. ThO₂, which -approximates to the formula Th(NO₃)₄,4H₂O; the commercial product, -however, is not a definite hydrate. Kolbe[484] has described the -additive product with antipyrine, 2Th(NO₃)₄,5C₁₁H₁₂ON₂, which melts at -168°. The extent to which thorium salts are hydrolysed in solution is -very considerable, as is evident from the fact that the nitrate may be -titrated with standard potash in presence of phenolphthalein as -indicator; the solution first becomes alkaline to this reagent when 3·5 -molecules of potash have been added for each molecule of thorium nitrate -present.[485] Of the large number of _double nitrates_ which have been -prepared, the general types R´₂Th(NO₃)₆, where R´ = NH₄,K,Rb,Cs, and -R´´Th(NO₃)₆,8H₂O, where R´´ = Mg,Mn,Zn,Ni,Co, are the most important. - - [484] _Zeitsch. anorg. Chem._ 1913, ~83~, 143. - - [485] Halla, _loc. cit._ - -_Thorium phosphates._--The precipitates obtained by addition of -phosphoric acid or alkali phosphates to solutions of thorium salts are -gelatinous solids of doubtful composition; they dissolve in mineral -acids and in alkali carbonates, and their behaviour is of great -importance in the technical treatment of monazite. Various phosphates -and _double phosphates_ are obtained by fusion methods, but none of -these are important. The _phosphite_, Th(HPO₃)₂,3H₂O, and -_hypophosphite_, Th(H₂PO₂)₄, are insoluble solids obtained by double -decomposition. The _hypophosphate_ ThP₂O₆,11H₂O, is of great importance -for purposes of detection and estimation, since it is thrown down -quantitatively from strongly acid solutions; under these conditions the -rare earths remain in solution. - -No neutral _carbonate_ of thorium is known. Alkali carbonates -precipitate a basic salt, which dissolves readily in excess; this fact -is of very great importance in the commercial extraction of thorium, the -sodium and ammonium double carbonates of the cerium elements being -almost insoluble in alkali carbonates. Addition of alcohol to the -solution throws down double carbonates, which can be washed with ice -water. The salts K₆Th(CO₃)₅,10H₂O, Na₆Th(CO₃)₅,12H₂O, and -(NH₄)₂Th(CO₃)₃,6H₂O have been obtained in this way; they dissolve -readily in water or dilute alkali carbonate, though on warming or -diluting the solution, the hydroxide separates. The thallium compound, -Tl₆Th(CO₃)₅, is sparingly soluble, and is thrown down from a solution of -the ammonium compound on addition of a thallium salt; it has been -proposed for the microchemical detection of thorium. The quantitative -separation of thorium by means of pure moist lead carbonate has been -proposed for the purpose of estimation (see p. 288). - -_Thorium oxalate_, Th(C₂O₄)₂,6H₂O, is precipitated quantitatively by -means of oxalic acid, even in presence of considerable quantities of -mineral acids. It is less soluble in sulphuric acid than any of the rare -earth oxalates,[486] and is not attacked, as are the latter compounds, -by concentrated nitric acid. In hydrochloric acid the solubility first -increases rapidly with the concentration of the acid, and then suddenly -decreases; this behaviour is due to the formation of an _oxalochloride_, -3Th(C₂O₄)₂,ThCl₄,20H₂O. When the amorphous oxalate obtained by -precipitation is allowed to remain for a considerable time in contact -with acids, it forms characteristic tetragonal prisms of the more stable -form. The dihydrate, Th(C₂O₄)₂,2H₂O, is obtained when the hexahydrate is -dried over sulphuric acid, or heated to 100°. The salt dissolves easily -in excess of alkali oxalate, but is precipitated from the solutions by -mineral acids, a fact which allows of another means of separation from -zirconium, the double oxalates of which are much more stable towards -acids. The solubility of the oxalate in alkali oxalate allows of -separation from the rare earth elements, whilst its insolubility in -excess of oxalic acid can be used for the separation from zirconium. - - [486] Hauser and Wirth, _Zeitsch. anorg. Chem._ 1912, ~78~, 75. - -The _formate_ and _acetate_ can be obtained in the form of neutral salts -by the action of the acids on the hydroxide; by double decomposition, -amorphous precipitates of basic salts are obtained. With _tartaric acid_ -stable complex compounds are formed, as shown by the fact that alkalies -will not precipitate the hydroxide from a solution in presence of that -reagent, and by the elevation of the specific rotatory power. Many -_complex salts_ are known, the simplest having the composition -ThO(C₄H₄O₆R´)₂,8H₂O, where R´ = K,Na,NH₄; these are obtained by -dissolving thorium hydroxide in concentrated solutions of alkali -hydrogen tartrates. _Thorium acetylacetone_, Th(C₅H₇O₂)₄, is -precipitated by addition of ammonia to an aqueous solution of the -nitrate mixed with acetylacetone dissolved in ammonia; the solid is -recrystallised from alcohol, and melts at 171°. - - -~Atomic Weight of Thorium.~--The value adopted by the International -Committee (1914) is 232·4, but most of the determinations carried out -within the last thirty years show considerable discrepancies. The -earlier work of Berzelius (1829) and Chydenius (1861) led to very widely -varying results, and for the same reason little reliance can be placed -on the results of Delafontaine (1863) and Hermann (1864). In 1874 Cleve -determined the constant by ignition of the sulphate, obtaining the mean -values 234·03 and 233·97; the figure 234 based on these results was for -many years accepted as the true atomic weight. A series of -determinations carried out by Nilson in 1882 led to much lower results. -He employed the sulphate ennea- and octohydrates, first dehydrating -these, and then igniting to oxide, and showed that Cleve’s value must be -too high on account chiefly of the hygroscopic nature of the ignited -oxide, which increases in weight when kept; but his own values show -considerable discrepancies. The ratio Th(SO₄)₂,9H₂O-ThO₂ : ThO₂ -(enneahydrate converted to oxide) gave the figure (corrected to vacuo) -232·51, whilst the ratio ThO₂ : 2SO₃ (anhydrous sulphate to oxide) gave -232·16; the ratio Th(SO₄)₂ : 9H₂O (hydrate to anhydrous salt) gave, -however, 233·75. The value obtained for the ratio ThO₂ : 2SO₃ for -anhydrous sulphate prepared from the octohydrate was 232·49 (corrected -to vacuo). Five years later, Krüss and Nilson prepared the anhydrous -sulphate from the pure octohydrate, and ignited this to the oxide. The -ratio ThO₂ : 2SO₃ gave as a mean of very concordant results the figure -232·49. - -Brauner criticises these values on the ground that no details are given -as to the temperature required to obtain the anhydrous salt from the -hydrates, and that probably some traces of sulphate must be decomposed -at the temperatures required (450°-500°) to drive off all the water. The -results obtained from the enneahydrate are to a great extent invalidated -by the doubts as to the purity of the hydrate, completeness of -dehydration, etc., which arise from the discrepancies in the values -deduced from the three ratios. He accepts, however, the figure 232·49 -obtained by Nilson and by Krüss and Nilson from material separated as -octohydrate, with some uncertainty as to the second decimal figure. - -Brauner himself employed the oxalate method in 1898; the purified -hexahydrate was used, the percentage of thoria being determined by -ignition, and of (C₂O₃) by titration with permanganate. The ratio ThO₂ : -2C₂O₃ gave results varying from 232·21 to 232·29, but as the value rose -continuously as purification was carried further and further, he did not -feel justified in taking a mean value. In 1900 Urbain determined the -constant with material purified by the acetylacetone method. He prepared -the octohydrate, heated it for ten hours in a bath of sulphur vapour at -440°, and ignited the anhydrous salt so obtained at a white heat. The -ratio ThO₂ : 2SO₃ gave the result (corrected to vacuo) Th = 233·67. -Brauner criticises the value on the ground that the hydrated salt was -heated in a vessel open to the air, and that at the high temperature -obtained, traces of moisture gaining access to the sulphate caused -hydrolysis, with loss of sulphuric acid; this would cause the results to -be too high. In 1905 Meyer and Gumperz employed the same method, and -obtained values varying from 232·2 to 232·7, with the mean 232·47. -Finally Brauner carried out an extended investigation to disprove the -heterogeneity of thorium which had been ‘discovered’ by Baskerville -(1904), in the course of which he showed the atomic weight of the -element to lie between the limits 232·34 and 232·52. - - -~Detection of Thorium.~--The element is best detected in a mixture of -earths by the following reactions: - -(1) Precipitation with hydrogen peroxide from warm, faintly acid -solution. - -(2) Precipitation with sodium hypophosphate, Na₂H₂P₂O₆, in concentrated -hydrochloric acid solution. On boiling, a perceptible precipitate is -obtained if only traces of thorium are present; but ceric and zirconium -salts and titanium must be absent. The latter element gives no -precipitate under these conditions if hydrogen peroxide is present; -ceric salts may be decomposed by boiling. The possible presence of -zirconium renders it necessary to boil the hypophosphate precipitate -with nitric acid; on addition of oxalic acid to the clear solution, -thorium is precipitated, whilst zirconium remains in solution, and may -be detected. - -(3) Potassium azide, KN₃, throws down thorium hydroxide from boiling -neutral or faintly acid solutions. Ceric salts if present must be -previously reduced; zirconium must be previously removed by oxalic acid. - -(4) Precipitation may be effected with potassium iodate in strong nitric -acid solution. Here also ceric salts must be reduced before applying the -test. Zirconium also gives the test; the precipitate must therefore be -washed and warmed with oxalic acid, in which thorium iodate is -insoluble, whilst zirconium iodate is soluble. - -The methods of estimating thorium are given in Chapter XVIII. - - - - -PART III - -THE TECHNOLOGY OF THE ELEMENTS - - -CHAPTER XVII - -THE INCANDESCENT MANTLE INDUSTRY--HISTORICAL AND GENERAL INTRODUCTION - -The group of elements which we are considering can be divided, from the -point of view of technical application, into two classes. The first of -these contains one element only, titanium, which in its technology, as -in its chemistry, stands apart from the others; it will, accordingly, be -treated in a separate chapter. The second class contains the yttrium and -cerium metals, with zirconium and thorium; the technical importance of -these elements is due chiefly to the use of their oxides in -illumination, to a small extent in Nernst lamps, and to a much greater -extent in the so-called Incandescent Lighting. The manufacture of -incandescent mantles[487] is a large and ever-extending industry, -intimately bound up with the older process of coal-distillation, with -its innumerable ramifications; indeed, it may be said that but for the -ingenious invention of Dr. Auer, illumination by means of coal-gas would -to-day have been almost obsolete. The discovery which resulted in the -production of the familiar incandescent mantle of the present day may be -regarded as the culmination of a century’s effort to increase the value -of coal-gas as an illuminating agent. In the present chapter it is -proposed to outline the history of these endeavours, and to give a short -general account of Auer’s work and its results. - - [487] The term ‘incandescent mantle’ is not, perhaps, scientifically - very desirable. It is used here, not only on account of its general - acceptance, but also because there seems to be no brief and convenient - term which might be used in its stead. - -Soon after the introduction of gas as an illuminating agent it was -realised that the luminosity of the flame is dependent on the presence -of solid particles, which by the heat of combustion of the gas are -raised to a temperature at which they emit radiations of wave-lengths -corresponding to the ‘luminous rays’ of the spectrum. A non-luminous -flame of sufficiently high temperature, therefore, can be rendered -luminous by the introduction of suitable solids, and numberless -investigators have striven, during the past century, to discover the -most suitable method of increasing the luminosity of a flame in this -way. The luminosity of the ordinary ‘bats-wing’ or ‘flat’ flame, now so -rapidly going out of use, is due to the presence in the outer zone of -the flame of heated particles of carbon, produced by the -decomposition--or partial combustion--of ‘dense’ hydrocarbons, _i.e._ of -hydrocarbons having a high percentage of carbon. Ordinary coal-gas -consists largely of a mixture of hydrogen and methane, both of which -burn with practically non-luminous flames, with small quantities of -olefines, acetylenes, etc., to which the luminosity is chiefly due. It -would appear, then, that by the introduction of dense hydrocarbons, a -gas of poor illuminating power might be made much more valuable as a -source of light. On the other hand, it is also apparent that the same -end might be achieved by the introduction into a non-luminous or feebly -luminous flame of an altogether foreign substance, introduced as such, -and not continuously consumed, as is the carbon in the former method. -Both these directions of improvement have been followed; since, however, -the results achieved by the latter method have become recently of far -greater importance, the applications of the first method will be -dismissed quite briefly, and the history of the second will then be -treated somewhat fully. - -The first important attempt to increase the illuminating power of gases -burning with feebly luminous flames was that of Faraday, who in the -course of an investigation into the causes of the variations in -luminosity of ‘portable gas,’ discovered benzene, or bicarburet of -hydrogen, as he called it, in 1826. In 1830 an engineer named Dunnovan -undertook to illuminate Dublin by means of water-gas[488] which he -‘carburised’ by addition of dense hydrocarbons. During the latter half -of the nineteenth century this method became of some importance. It has -been applied, in particular, to enrich the ‘natural gas’ of Ohio, North -America. The dense hydrocarbons necessary for this purpose are obtained -by the process known as ‘cracking.’ The viscous residues from the -distillation of the mineral oil of the district are allowed to drop into -a brick chamber, of which the walls are raised to a bright red heat, and -the dense hydrocarbons which are evolved are removed by a current of the -gas to be enriched. In this way a gas of relatively high illuminating -power is obtained. - - [488] Water-gas is a mixture of equal volumes of carbon monoxide and - hydrogen, obtained by blowing steam through a glowing coke furnace. At - intervals the steam is shut off, and air is blown through to raise the - temperature of the coke. - -In the year previous to that in which Faraday first carburised -water-gas, Berzelius had observed that thoria and zirconia, when heated -in a non-luminous flame, emit an intense white light. Similar behaviour -had long before been observed in the cases of magnesia, alumina, lime, -zinc oxide, etc. The first practical application of this property of the -oxides was that of Drummond, who in 1826 heated a pencil of lime in the -oxy-hydrogen flame and obtained the intense white light which has since -become so familiar as the Drummond or ‘lime-light.’ A further -development in this direction was due to du Motay and Maréchal, who in -1867 illuminated the Place de Tuileries and the Hôtel de Ville in Paris -by means of pencils of compressed zirconia--magnesia was also -used--heated by means of oil vapour and oxygen. - -The use of non-luminous flames to secure illumination, by raising the -temperature of solids suspended in them to the point of incandescence -was proposed in 1839 by Cruickshank, who used a mantle of platinum wire, -covered with lime and rare earths, which he heated by means of -water-gas. In 1846 Gillard employed mantles of platinum wire, raised to -incandescence in the flame of burning hydrogen, which he obtained by -passing steam over heated iron wire; later he used water-gas (1848), his -lamps with this modification being employed in Paris and in -Philadelphia. Narbonne was later illuminated (1856-1865) by a similar -device, but permanent success could hardly be obtained in view of the -cost of the platinum mantles, which lasted only a few months. The same -mantle was proposed in 1882 by Lewis, the ordinary Bunsen flame being -suggested as the source of heat. In the same year Popp exhibited at the -Crystal Palace lamps in which a platinum mantle was raised to -incandescence by means of a flame of coal-gas and heated air. These -attempts, however, served only to show that no permanent advance could -be made in this direction. - -A new development was made in 1880 by Clamond. He prepared a paste by -grinding up calcined and powdered magnesia with a concentrated solution -of magnesium acetate; by forcing this through a press he obtained a -ribbon which was then wound crosswise on a wooden shaper, dried -carefully, and ignited. In his later experiments twenty per cent. of -zirconia was added to the magnesia. The mantle was supported in a -platinum cage and heated in the flame of a mixture of coal-gas and -heated air. This mantle gave an intense light, but was too fragile for -extended use. In the following year, Lundgren patented a process by -which lime, magnesia, and zirconia, made into a paste by the addition of -gum, were forced through a press, and the resulting thread wound on a -graphite-covered shaper. The mantle so obtained was stable, and gave an -intense white light, but after having been heated for some time the -oxides crumbled to powder. A modification of this process was introduced -by Knöfler in 1894, in an attempt to use a cellulose solution containing -rare earth salts; this was forced through jets, and the cellulose -precipitated as a continuous thread from which the mantle was made. A -further modification of Knöfler’s process by Plaisetty in 1901 was -technically successful; but these developments must be taken up in a -later chapter (_vide_ p. 307). - -In 1883 a process was patented by Fahnehjelm in Stockholm, by which for -the first time a cheap and stable mantle of considerable efficiency was -produced, and which, but for the advent of the Auer mantle, would -undoubtedly have been commercially successful. Fahnehjelm’s mantle -consisted of an arrangement of needles or lamellæ of magnesia, lime, -zirconia, etc., suspended over a burner. The plates and needles were -usually arranged in the form of a comb of suitable shape, and were found -to give an intense light, and to be long-lived. In later forms the combs -were made of rods of magnesia dipped into solutions of chromium salts. -The great disadvantage of this invention lay in the fact that the combs -required to be heated in the flame of water-gas, in order to secure a -good incandescence; had it been possible to attain a sufficiently high -temperature by the use of coal-gas, it is doubtful whether the Auer -mantle would have ever been evolved. - -The more important attempts to secure arrangements by which the -radiations of heated solids could be used for illumination have now been -outlined and the ground cleared for the consideration of the work of -Baron von Welsbach. There remain yet to be mentioned, however, two -attempts which are of especial interest in view of that work. The first -is that of Frankenstein, who in 1849 made use of a ‘Light-multiplier’ -obtained by impregnating gauze with a paste of chalk and magnesia ground -with water. The second is that of Edison, who proposed (1878) to utilise -the observations of Bahr and Bunsen (1864) and of Delafontaine (1874), -of the remarkable incandescence exhibited by the yttria and erbia -earths, and the terbia earths, respectively, when heated; he suggested -the employment of a mantle of platinum wire covered with zirconia and -the oxides of the rare earth metals, a proposal similar to that put -forward nearly forty years earlier by Cruickshank. - -About the year 1880 Dr. Carl Auer began the study of the rare earth -elements. The chemical aspect of his work has already been dealt with -(_vide_ p. 168); but the results obtained by the technical application -of his observation that threads of cotton, impregnated with a solution -of salts of the elements, leave after ignition a coherent ash of oxide, -which glows brightly when heated, have been of far greater importance -than the purely scientific aspect, valuable though that is. A series of -experiments soon showed that a fabric of suitable shape, impregnated -with a solution of nitrates or acetates of the rare earth elements, -after being dried and drawn together at one end by means of a platinum -wire, can be ignited in a Bunsen flame in such a way as to leave a -coherent skeleton of the earth oxides, which can be formed and hardened -by suitable manipulation with a high temperature burner; the mantle so -prepared, when suspended from a lateral support in a Bunsen flame, gives -a light of considerable intensity, the colour varying with the oxides -employed from green to orange tints. - -The earlier mantles, which were placed on the market about 1883, -consisted chiefly of oxides of lanthanum and zirconium, with smaller -quantities of the other oxides, selected according to the shade of light -desired. These mantles were protected by patents taken out in France in -1884, and in Germany in 1885 and the following years. The process[489] -was briefly the following: A vegetable fibre, of cylindrical form, woven -from threads of about 0·22 mm. diameter, is washed with dilute -hydrochloric acid, then with distilled water, and impregnated with a 30 -per cent. solution of the selected salts. The fabric is then wrung out -and dried, and cut into suitable lengths, allowance being made for -subsequent shrinkage. One end of each cylinder is then drawn together by -means of a platinum wire, and the mantle hung from a side support over a -burner and incinerated. The head is then treated with a solution of -aluminium and magnesium nitrates (beryllium nitrate and the -corresponding phosphates are also specified) to strengthen it, and the -mantle dried, and ‘formed’ by means of a very hot flame. This first -patent protected several definite mixtures of salts, chosen so that the -mantle should emit light of a definite known tint. The chief oxides -employed were lanthana, yttria, magnesia, and zirconia. A German patent -granted in 1886[490] protects the use of thorium salts, and a long list -of salts of the elements with numerous acids; an important advance -mentioned in this specification is the process of collodinisation of the -finished mantle, by dipping in a solution of rubber in benzene or of -collodion (cellulose nitrate) in ether and alcohol, which renders the -product strong enough for transport. From 1885 to 1891 numerous -improvements were effected; asbestos threads were substituted for -platinum wire, central rods of magnesia replaced the lateral platinum -support, and various mixtures of oxides were tried. None of the -innumerable mixtures employed, however, was successful in establishing -the struggling industry on a firm basis in face of the vigorous -competition of the electric lamp, and it was not till 1891 that the -introduction of the final ‘Auer Mixture,’ which is in use at the present -day, gave the welcome assurance of a certain success to von Welsbach and -his assistants. The discovery of this mixture was a result of the -examination of a quantity of impure thoria; it was found that mantles -made from the nitrate gave a light which steadily decreased in intensity -as the impurities were removed. It needed only the observation that the -impurities consisted chiefly of cerium compounds to turn the long and -arduous investigation in the direction of final success, and our present -mantles, which consist approximately of 99 per cent. thoria and 1 per -cent. ceria, were placed on the market in 1891, the composition being -announced by patent in 1893.[491] - - [489] _Vide_ _D. R. P._ 39162. Granted September 23, 1885. - - [490] _D. R. P._ 41945. - - [491] _Vide_, _e.g._ Moeller, _E._ 124, 1893. - -The effect of increasing or decreasing the ratio of the two oxides, and -the theories which have been advanced to account for the results, must -be referred to in a later chapter (_vide_ p. 294). It may be mentioned -here, however, that practically no other known mixture gives such -satisfactory results, though mantles have been manufactured of alumina -with small quantities of chromic oxide, and ‘inverted’ mantles made of -these oxides with zirconia have recently been advocated by Professor -Lewes,[492] an authority on gas lighting. Mixtures of alumina and -uranium oxide have also been patented, but no mantles appear to have -been manufactured according to the specifications. In this connection, -also, may be mentioned the various attempts to evade the Auer patents by -taking advantage of the ‘discovery’ of ‘new’ elements. One enterprising -firm, after having an account of a ‘new’ element, Lucium, inserted in a -well-known scientific periodical, put salts on the market, and proceeded -to manufacture mantles from what were proved by analysis to be cerium -compounds. Similar ‘new’ elements were Russium, Kosmium, and -Neo-kosmium, names which covered various mixtures of thorium and cerium -compounds with other salts. - - [492] _Vide_ _D. R. P._ 218333 of January 1910. - -After the introduction in 1891 of the final Auer mixture, progress -became rapid. The original mantles, made from cotton, had many -disadvantages; thus after being in use for some time they were found to -shrink considerably, with marked decrease in strength and light-giving -power. Once the success of the new form of lighting was assured, -numberless investigations were undertaken to lengthen the life and -increase the efficiency of the mantles. The most important of these were -connected with the endeavour to replace cotton by some fabric which on -ignition would leave the oxide skeleton in a harder, more coherent and -more elastic condition. The first great advance in this connection was -the introduction of Ramie fibre by Buhlmann in 1898. Ramie, China-grass, -or grass-cloth, as it is sometimes termed, is a fabric made from the -fibres of the tschuma plant of the Yang-tse-kiang valley and other parts -of Asia; mantles made from it last longer and maintain their efficiency -much better than the earlier cotton mantles, which they have very -largely displaced. The use of artificial silk was patented by De Mare in -1894, but his process was unworkable; it was an effort to adapt to the -purposes of incandescent lighting the nitro-cellulose process introduced -by Chardonnet in 1890 for the manufacture of artificial silk. In 1897 De -Lery and in 1900 Plaisetty made further efforts in this direction, and -finally in 1902-1903 the latter worked out a process by which mantles -were made directly from the spun fabric. These mantles are superior in -every way to the earlier ramie or cotton kinds, and are rapidly coming -into general use, especially for lamps using high-pressure gas. -Numberless patents for the manufacture and improvement of this kind of -mantle have been taken out during the last ten years; the most important -of these will be dealt with in a later chapter. - -Attempts have been made to secure greater strength and toughness in -mantles in other directions also. The use of metallic wires in the fibre -has been suggested; numerous patents deal with mantles ‘strengthened’ by -doubling the thread at intervals, and by special methods of weaving the -fibre. One method, which follows on the lines of Glamond and Lundgren, -proposes[493] the use of mantles made from various oxides mixed with -silica, the whole being worked into a paste by use of a gum or soap, -from which threads are prepared by pressure; mantles made from these -threads are said to be very strong and porous. Another patent[494] -protects the manufacture of ‘incandescence bodies’ made from plates or -combs prepared from a thread obtained in a rather similar way. A third -of these innumerable suggestions recommends a preliminary impregnation -of the fabric with an aluminium or magnesium salt,[495] from which the -oxide is precipitated on the fabric by a suitable means, impregnation -with the ordinary ‘lighting fluid’ being effected after drying. Quite an -early patent[496] proposes the impregnation of the prepared mantle, -either after or just before burning off, with an alcoholic solution of -an organic silicon compound, so that when the mantle is in use a -skeleton of silica is formed to ‘strengthen’ the oxide ash. No useful -purpose can be served by extending the list of these proposals; enough -has been said to indicate the various directions in which so many vain -attempts at improvement have been made. - - [493] Laigle, _D. R. P._ 216871 of December, 1909; see also _D. R. P._ - 216877 and 219640. - - [494] Michaud and Delasson, _D. R. P._ 210640, June, 1909; see also - _D. R. P._ 227257. - - [495] Zdanowich, _E._ 27755, 1908. - - [496] Jasper, _E._ 30145, 1897. - -From the mechanical and physical side the recent developments have been -very marked. The introduction of the ‘inverted’ lamp was a tremendous -step forward, and paved the way to the second great improvement, the use -of ‘high-pressure’ gas, with which such successful results are being -obtained. The form of lamp now coming into use for street lighting gives -1500 candle-power per mantle, and usually carries three mantles; each -lamp thus develops 4500 candle-power. The purely mechanical devices -which are now used to secure ‘automatic’ lighting are rapidly bringing -this form of lamp into favour for street illumination. A full account of -these developments would be entirely beyond the scope of the present -work. In the following chapters, therefore, no complete treatment of the -incandescent lighting industry can be given; but whilst the chemical -aspect is treated at some length, many points of more purely technical -character, which are connected with this, have also been included. - - -CHAPTER XVIII - -THE CHEMICAL TREATMENT OF MONAZITE - -It has been stated in the previous chapter that the first Auer mantles -were made of mixtures of various rare earth oxides, the mixture of -thoria with 1 per cent. of ceria being first employed in October, 1891. -The impetus given to the mantle industry by the success of the new -mixture caused an immediate demand for thoria, which was at that time -extracted from thorite (see p. 43). A ‘thorite-fever’ broke out along -the coasts of Scandinavia, and the price of orangite rose to 600 marks -per kilogram (about £13 10_s._ per pound avoirdupois), sinking again -shortly to 80 marks[497] (about £1 16_s._ per lb). The discovery of the -monazite sands of the Carolinas and Brazil, which at the present rate of -consumption may be considered to be, for all practical purposes, -inexhaustible, placed the industry on a firm basis, and the pure -monazite, extracted from these deposits by the methods outlined in -Chapter VII, is now almost the sole source of the thorium nitrate of -commerce. Small quantities are obtained from thorianite, the separation -of the pure material presenting, in this case, very little difficulty by -reason of the solubility of the mineral in acids and the very high -percentage of thoria. - - [497] _Vide_ Böhm, ‘Die Thorium Industrie,’ _Chem. Ind._ 1906, ~29~, - 450 and 488. - -The extraction of pure thorium compounds from monazite is a process of -very great technical difficulty. The percentage of thoria is small, -whereas that of the ceria oxides is high. The mineral is almost always -decomposed by heating with concentrated sulphuric acid, and when the -resulting pasty mass is taken up with water, a large amount of free -sulphuric acid must be present in order to hold the rare earth -phosphates in solution. For the separation of thoria from ceria and -yttria compounds in acid solution no processes were known until quite -recently. When it is remembered that the thorium nitrate used for the -manufacture of mantles must be of a degree of purity which very few -commercial products ever approach, some idea of the difficulties of the -extraction may be obtained. - - -~Decomposition of the Monazite.~--Two processes have been used for the -working up of monazite. The first of these consists in fusing the -mineral with soda, and extracting the sodium phosphate with water; the -earths may then be taken into solution with acid, and the separation -effected as outlined below. This method is very rarely used. A process -has been proposed, in which the monazite is fused with carbon in an -electric furnace; the cooled mass is treated with mineral acids, which -take the earths into solution free from phosphoric acid. No technical -application has so far been made of this proposal. - -The method commonly used is that in which the sand is decomposed by -means of sulphuric acid. The charge usually employed, about two to three -hundred kilograms, requires from four to six hours’ heating, about twice -the weight of concentrated acid being needed. The operation is carried -out in cast-iron vessels, and an efficient draught must be maintained to -remove the acid fumes; the factories are usually isolated. The treatment -with sulphuric acid converts the phosphates chiefly into sulphates; when -the reaction is finished, the liquor fumes strongly and begins to -thicken, heating being stopped when a thick broth is obtained. The -cooled mass is extracted with water, care being taken to maintain a -degree of acidity sufficient to prevent any precipitation of the -phosphates. - -It has been already stated in Part I (_vide_ p. 73) that a strongly -radioactive product. Radiothorium, has been obtained from the mineral -thorianite. This body is produced by the atomic degradation of thorium, -and an intermediate body, mesothorium, has been found to be formed -during the change. Mesothorium is a substance which, though it appears -to be chemically identical with radium, has an activity equal to three -hundred times that of radium, and when in equilibrium with its -degradation products the ‘rays’ it emits are very similar to those of -the latter element. Since mesothorium is a degradation-product of -thorium, it occurs in minute quantities in all thorium minerals, and by -reason of the possibility of using it as a substitute for radium, its -extraction becomes a matter of importance. Soddy[498] has shown that if -a barium compound be added to monazite before the treatment with -sulphuric acid, the mesothorium remains with the barium sulphate; this -is readily separated from the heavy unchanged grains of sand, and is -purified, and finally obtained as chloride by treating the solution with -hydrogen chloride. On recrystallisation of the barium chloride, the -active products are concentrated in the less soluble part, and it is -possible to prepare on the commercial scale a mixture which, though it -contains only 0·25 per cent. of mesothorium, has an activity equal to -that of pure radium bromide. This mixture contains 25 per cent. of -radium compounds, radium being present as an original constituent of -monazite; owing to the chemical identity of radium and mesothorium,[498] -the latter cannot be separated, but Soddy, by removal of much of the -barium compound in the laboratory, has obtained a product four times as -active as the pure radium salt. - - [498] _Proc. Chem. Soc._ 1910, ~26~, 336, and _E._ 25504, November, - 1910. See also Hahn, _Chem. Zeitg._ 1911, ~35~, 845. - -It is probable that the treatment of monazite will in the future be -modified by the addition of barium sulphate before the sulphuric acid -decomposition, to allow of the commercial extraction of its mesothorium. - - -~Separation of Thorium.~--The separation of a crude thorium product from -the acid solution obtained after decomposition of the mineral can be -effected in two ways, both of which are based on the fact that thoria is -less basic than the oxides of the cerium and yttrium metals. In the -first, the rare earth elements, including thorium, are precipitated as -oxalates by the addition of oxalic acid to the acid solution. These are -again taken into solution by the action of hydrochloric acid on the -hydroxides, obtained by prolonged digestion of the oxalates with sodium -hydroxide; the acid solution is then treated carefully with sodium -hydroxide, or pure powdered magnesia, until about one-sixth of the bases -has been precipitated, the liquid being constantly stirred. Thorium -hydroxide being very weakly basic is precipitated before the other -hydroxides, and the precipitate obtained, after one or two repetitions, -contains most of the thorium originally present in the monazite. In the -second process, thorium is partially separated from the other metals by -adding gradually to the solution obtained after the treatment of the -mineral with sulphuric acid, the quantity of magnesia calculated to -precipitate a suitable fraction of the earths, with constant stirring; -this throws down a mixture of phosphates containing almost all the -thorium and some of the other elements. The slimy phosphate precipitate -is dissolved in hydrochloric acid, and the earths precipitated as -oxalates; the precipitate must be washed thoroughly in order to remove -phosphoric acid. It will be seen that these two methods differ only in -that in the first the phosphoric acid is removed before the -precipitation of thorium, whereas in the second the thorium is -precipitated as phosphate, and this transformed into oxalate. - -Quite recently, methods have been proposed by which the thorium can be -separated in a fairly pure condition from the acid solution obtained -from the sulphuric acid treatment. Rosenheim, Meyer and Koppel[499] -protect the use of hydrofluosilicic acid (H₂SiF₆), and its salts, for -this purpose. The sodium salt, added to the hot acid liquid, produces a -quantitative separation of thorium silicofluoride; the precipitate is -washed by decantation, and treated with sulphuric acid, the thorium -sulphate being then purified directly by the sulphate method described -below. A second method proposes to make use of the insolubility of -thorium hypophosphate, ThP₂O₆,11H₂O, which was found by Kaufmann in 1899 -to be insoluble in water, and in acids and alkalies. This method has -already been in use for some years for analytical work;[500] it appears -to be readily susceptible of adaptation for the technical -extraction,[501] the sodium hypophosphate, Na₂H₂P₂O₆,6H₂O required as -the precipitating agent being obtainable in large quantities by the -electrolytic oxidation of copper phosphide, employed as the anode in an -electrolytic cell.[502] This method also gives a thorium compound -sufficiently free from other earths to be subjected at once to the -refining process; the hypophosphate has in fact been suggested as a very -suitable compound for the impregnation of artificial silk mantles -directly. The thorium nitrate of commerce, however, is still prepared -almost entirely from the crude product obtained by one or other of the -two methods of fractional precipitation first described, so that it -becomes necessary to outline the method generally employed for -separating from this a compound pure enough to be suitable for the final -refining process. - - [499] _D. R. P._ 214886, October, 1909. - - [500] Rosenheim, _Chem. Zeitg._ 1912, ~36~, 821; also Koss, _ibid._ - 686 - - [501] Wirth, _Zeitsch. angew. Chem._ 1912, ~25~, 1678. - - [502] Rosenheim and Pinsker, _Ber._ 1910, ~43~, 2003. - -The crude oxalate or hydroxide is thoroughly digested with a -concentrated solution of sodium carbonate. The carbonates of the cerium -elements are much less soluble in sodium carbonate solution than is -thorium carbonate. After thorough digestion the liquid is filtered from -the undissolved carbonates. The thorium is reprecipitated from the -filtrate, either as oxalate, by the addition of hydrochloric acid (if -the crude material was in the form of oxalate), or as hydroxide, by the -addition of sodium hydroxide. The process is again repeated, and a final -digestion is then made with ammonium carbonate; addition of an alkali to -the clear filtrate now gives thorium hydroxide sufficiently pure to be -used for the last refining. - - -~Purification of the Thorium Compounds.~--The object of this last stage -is to remove from the thorium compound small quantities of cerium and -yttrium salts which cannot be separated by the carbonate method. The -chief process is the sulphate crystallisation, the principles underlying -which have been thoroughly examined in the patient researches of Koppel -and Holtkamp.[503] Since the process is based on the solubilities of -the various thorium sulphate hydrates, it is necessary to consider these -in some detail. - - [503] _Zeitsch. anorg. Chem._ 1910, ~67~, 266. - -The solubility-curve of thorium sulphate was examined by Demarçay and by -Roozeboom. Three important hydrates are known, viz. Th(SO₄)₂,9H₂O, -Th(SO₄)₂,8H₂O, and Th(SO₄)₂,4H₂O, other unstable intermediate compounds -being said to exist. From a study of the diagram it will be seen that -the hydrate with 8 molecules of water is labile, whilst the 9-hydrate -and the 4-hydrate have a transition temperature at 43°C., the transition -temperature of the 8-hydrate and the 4-hydrate being just below this. - -[Illustration: FIG. 10] - -Since the 8-hydrate is labile with regard to the 9-hydrate, and the -transition temperatures are so near, the former will be formed first as -a solution cools, and by reason of the great similarity of the -solubility-curves for the 9- and 8-hydrates the rate of change of this -to the 9-hydrate will be very slow. In practice, therefore, it is always -the 8-hydrate which is formed, and it is on the separation of this -compound that the success of the process depends. The anhydro-compound, -Th(SO₄)₂, which can be obtained by heating any of the hydrates to -300°-400°C., is very soluble at 0°, but slowly hydrates itself and -separates from the solution as the 8-hydrate, which has a very low -solubility. The sulphates of the cerium metals, compounds of which form -the chief impurities to be removed, are considerably more soluble, and -can be separated by repeated crystallisations. - -The thorium hydroxide to be purified is dissolved in sulphuric acid, and -in the first form in which the method was employed, the thorium sulphate -obtained by evaporation of the solvent was heated until it became -anhydrous. This was dissolved to saturation at 0°, and the solution -raised to the boiling-point, the 4-hydrate being precipitated; this -treatment was repeated several times. It was pointed out by Bunsen, from -theoretical grounds, that this method could never yield a pure thorium -salt, and Krüss and Nilson accordingly introduced a modification. The -impure sulphate, after dehydration, as before, is dissolved at 0°, and -allowed to come to ordinary room temperature, 20°; the hydrate which -separates (the 8-hydrate) is collected and dried at high temperature and -the crystallisation repeated. This method gives a fairly pure salt after -three recrystallisations, but the process is very tedious, owing to the -time required for drying and heating the hydrate. For this reason the -method was further modified by Cleve and Witt. The crude sulphate is -boiled with ammonia, and the hydroxide obtained dissolved in -hydrochloric acid; addition of sulphuric acid to the concentrated -solution in the cold transforms the chloride into the sulphate, which -separates as the 8-hydrate at ordinary temperatures. Three repetitions -give a satisfactory product, and in this form the method is now much -used. - -The work of Koppel and Holtkamp referred to above has placed the process -on a sound basis. These authors have examined the solubilities of the -various hydrates in presence of hydrochloric, nitric, and sulphuric -acids, and mixtures of these, at different temperatures. They find that -hydrochloric acid is to be preferred to nitric acid, in the process of -Cleve and Witt, as besides its lower price, its use involves less loss -than that of the latter acid; excess of hydrochloric acid is not -harmful within wide limits, whilst a slight excess of sulphuric acid -over the quantity required to form the sulphate is desirable, to secure -the greatest yield. Finally, the temperature at the addition of the -sulphuric acid must not be allowed to rise above 25°, for in the -presence of so much acid the transition temperature to the 4-hydrate, -normally 42°, is considerably lowered; it is necessary to avoid -separation of the 4-hydrate, which is a flocculent unworkable -precipitate. - -Recently it has been proposed to carry out the purification by use of -alkyl hydrogen sulphates,[504] as it is stated that the differences of -solubilities of the alkyl sulphates of thorium and the cerium metals are -greater than in the case of the sulphates themselves. It is also claimed -that the presence of a small quantity of the alkyl sulphate in the -thorium nitrate which forms the final product has a good effect on the -quality of the mantles made from it. - - [504] Kreidl u. Heller, _D. R. P._ 233023, March, 1911; _F._ 414463, - June, 1910. - -Another process of purification which has found considerable commercial -application is the acetate crystallisation, thorium acetate being -considerably less soluble than the acetates of the cerium elements. The -impure hydroxide is dissolved in acetic acid and the solution evaporated -to dryness; repeated washing with small quantities of water removes the -cerium acetates, and a fairly pure salt is obtained. This is repeatedly -damped with nitric acid and heated to dryness, but even after this -treatment a certain amount of unchanged thorium acetate is usually -present. - -In a second form of this method, due to Haber, the impure hydroxide is -dissolved in hydrochloric acid, and the acetate precipitated by addition -of sodium acetate. The precipitate is filtered off and re-dissolved in -acid, and the acetate again thrown down by means of sodium acetate. The -precipitate is then dissolved in nitric acid, and the solution -evaporated to dryness. In this form the method gives very good results, -even from a comparatively crude product; but the process is, of course, -considerably more expensive than the sulphate purification. - -The high price of the necessary reagents, again, is a bar to the -technical application of the very simple and efficient process of -Wyrouboff and Verneuil. These authors suggest the precipitation of -thorium peroxide from a warm dilute neutral solution by means of -hydrogen peroxide, a process which is quantitative and yields a very -pure product. The last traces of the cerium metals can be completely -removed by a second precipitation. The cost of hydrogen peroxide is too -high, however, to allow its employment on such a large scale, and the -method has not, in consequence, come into general use. - -The thorium nitrate obtained after purification by the sulphate method, -or by the less generally employed acetate method, is usually considered -sufficiently pure for technical purposes. Even now, however, it may -contain traces of sulphate, of iron, of alkalies, and of cerium metals. -If absolute purity is desired, the salt may be dissolved, and freed from -all impurities, except the cerium compounds, by precipitation with -ammonium oxalate and thorough washing; the oxalate may then be dissolved -in chromic acid, and potassium chromate solution added drop by drop; the -precipitated thorium chromate is nearly free from other rare earth -compounds, and repetition of the process will give a pure salt. The -separation from cerium metals may also be effected by the hydrogen -peroxide process. If the technical processes are carefully carried out, -however, a thorium nitrate of a very high degree of purity may be -obtained, and the laboratory purification need only be undertaken if -material is needed for very accurate quantitative work. - - -~Preparation of Thorium Nitrate from Mantle-ash.~--Since the ordinary -incandescent mantle, in use, consists only of the pure thoria and ceria, -with small quantities of alumina, lime, and magnesia, which have been -employed to strengthen the ‘head,’ the working-up of mantle-ash gives an -easy means of obtaining the nitrates, and high prices are accordingly -paid for the ash in quantity. At one period of great competition between -rival manufacturers, canvassers went from house to house in many large -towns buying up mantle residues, to be used for the extraction of the -thorium for ‘lighting-fluid.’ - -For this purpose, the oxides are treated with hot concentrated sulphuric -acid, the cooled residue dissolved in water, and the thorium and cerium -precipitated free from compounds of aluminium, magnesium, and calcium by -oxalic acid. If pure thorium nitrate, free from cerium, is required, the -oxalates are added to the last precipitate from the double carbonate -purification in the treatment of monazite (_vide supra_), and the -ordinary processes of refinement continued; more often, however, the -mixed nitrate for impregnation of the mantle-fabric is required, and -this is obtained by ignition of the oxalates and solution of the oxides -so obtained in nitric acid, more cerium nitrate being added if -necessary. - - -~Extraction of Cerium Nitrate.~--Since monazite is primarily a phosphate -of the cerium metals, the percentage of thoria being usually quite low -(_vide_ Monazite, Chapter VI), very large quantities of compounds of the -cerium group of elements are annually produced in the process of -extraction of thorium. There is at present a very limited demand for -these compounds (_vide_ Chapter XXI), no important uses having yet been -found for them. In the ordinary process of extraction of the thorium, -these elements remain as the sparingly soluble double carbonates, whilst -the thorium double carbonate is removed in solution. From the mixed -salts which contain 50-60 per cent. of the cerium compound, the cerium -nitrate required for the manufacture of mantles is prepared, but the -amount so used is a small fraction of the whole, and large quantities of -compounds of cerium and the allied elements are available as soon as -profitable uses can be found. - -Three processes are in general use for the preparation of cerium nitrate -from the mixed carbonates; all of these are based on the fact that -cerium can become tetravalent, forming in this condition compounds which -can readily be separated from those of the allied elements, which can be -obtained only in the trivalent condition. When ceria is dissolved in hot -nitric acid, ceric nitrate, Ce(NO₃)₄, is formed, though the action of -nitric acid on cerous carbonate or oxalate gives rise to cerous nitrate. -Two of the three processes are based on this reaction, and for these the -mixed carbonates are dissolved in hydrochloric acid, freed from foreign -elements by precipitation with oxalic acid, and the oxalates ignited to -the oxides, which are then dissolved in the required quantity of nitric -acid. In the first process the cerium is precipitated from this solution -by merely pouring it into a large excess of very dilute nitric acid, -when a yellow basic ceric nitrate is precipitated; this is washed with -dilute nitric acid by decantation, dissolved in concentrated acid, and -purified by a second precipitation in the same way. In the second -process, separation is effected by addition to the nitric acid solution -of the calculated quantity of ammonium nitrate; the solution is -concentrated to incipient crystallisation, and on cooling the double -ceric ammonium nitrate, Ce(NO₃)₄,2NH₄NO₃, separates. This is collected, -washed with dilute nitric acid, and recrystallised until a pure salt is -obtained. The double nitrate can be readily decomposed by ignition, -leaving ceria, which is dissolved in nitric acid; the nitrate is -obtained by evaporation. - -The third method, due to Drossbach, is based on the oxidation of cerium -salts in neutral solution by potassium permanganate. The mixed -carbonates are dissolved in hydrochloric acid, a further quantity of the -carbonates stirred in, to neutralise excess of acid, and a solution of -the required quantity of potassium permanganate added. The reaction is -said to proceed according to the equation: - - 3Ce₂O₃ + 2KMnO₄ + H₂O = 6CeO₂ + 2KOH + 2MnO₂ - -The precipitated solid is separated, and dissolved in acid; the cerium -is then precipitated as the oxalate, which is transformed into nitrate -in the usual way. The solution contains the other elements of the cerium -group, which are precipitated by means of sodium hydroxide. The yield -obtained by this method is very good, practically the whole of the -cerium being separated without loss; whilst it has the further advantage -that the remaining elements of the group can be precipitated at once -after the separation. - - -~Analysis of a Monazite or Monazite Sand for Thorium.~--Since the -commercial value of a monazite sand or concentrate, or of the pure -mineral, depends, at present, entirely on the percentage of thoria, it -is important to have a rapid and reliable method of estimating this -constituent. The only reliable methods of quantitatively decomposing -the mineral, however, all involve acid treatment, and excess of acid -must always be present to prevent precipitation of phosphates. Until -recently, no way was known for estimating thorium in an acid solution, -and all the earlier methods therefore involved tedious processes for -complete removal of phosphoric acid, so that the salts could be obtained -in neutral solution. This was usually effected by precipitation of the -whole rare earth content with oxalic acid, and thorough washing of the -oxalates; these can then be dissolved directly in fuming nitric acid on -the water-bath, or ignited to the oxides, which may then be dissolved in -the same reagent. The solution of nitrates is evaporated to dryness, to -effect removal of the excess of acid, the nitrates dissolved in water, -and the thorium estimated in the neutral solution. - -Among the earliest methods employed for the estimation in neutral -solution was the thiosulphate precipitation.[505] Thorium thiosulphate -is not known; when sodium thiosulphate is added to a neutral solution of -a thorium salt, a precipitate of thoria mixed with sulphur is obtained, -by hydrolysis of the potential thiosulphate, and decomposition of the -unstable thiosulphuric acid. The method, however, leaves much to be -desired; other earths are partly precipitated, and the separation of -thoria is not complete. For analytical purposes the precipitate obtained -is redissolved in hydrochloric acid, and a second precipitation with -thiosulphate effected. The filtrates from the two precipitations are -collected, and the whole earth-content precipitated from these with -ammonia; the hydroxides are dissolved in hydrochloric acid, and again -treated with thiosulphate to throw down any thoria which has escaped the -previous precipitations. The three precipitates of thoria are then -collected, dried, and ignited for weighing as pure thorium dioxide, -ThO₂. - - [505] Full accounts of this and the two following methods will be - found in an important paper by Benz, _Zeitsch. angew. Chem._ 1902, - ~15~, 297 - -Even more tedious and unsatisfactory is the method based on the -solubility of thorium oxalate in excess of ammonium oxalate in neutral -solution. The solution is boiled, ammonium oxalate added, and after some -moments a small quantity of ammonium acetate solution. On cooling, the -oxalates of the cerium metals separate, and can be collected; thoria is -precipitated from the filtrate by addition of ammonia. The process must -be repeated two or three times, the solution being allowed to stand for -one or two days each time, and finally the thoria must be precipitated -by thiosulphate to remove traces of the other bases before it can be -weighed. Benz (_loc. cit._) gives a complete account of this method, and -quotes numerous analyses carried out to test its accuracy. - -Far more satisfactory than either of the above is the peroxide method -used by de Boisbaudran and Cleve, and later by Wyrouboff and -Verneuil.[506] Thorium is completely precipitated as a ‘peroxide salt’ -(Th₂O₇,SO₃ or Th₂O₇,N₂O₅ respectively) from warm neutral solutions of -the sulphate or nitrate on addition of dilute hydrogen peroxide, a -second precipitation being necessary to free it from cerium compounds. -Wyrouboff and Verneuil state that the process is rendered difficult by -the fact that the peroxide cannot be converted into the dioxide by -heating, either alone or with acids, as decrepitation takes place and -may cause loss; they accordingly reduce the compound in presence of -hydrochloric acid by ammonium iodide, and precipitate thorium hydroxide -by ammonia. Benz (_loc. cit._) does not find this difficulty; he states -that small quantities of the peroxide dissolve easily in acids without -loss, and further finds that if an ammonium salt be added to the neutral -solution of the thorium compound before addition of hydrogen peroxide, -the precipitate forms much more readily and is very easily handled. -Borelli[507] states that the precipitated peroxide can be ignited -without loss to the dioxide, and weighed as this. - - [506] _Compt. rend._ 1898, ~126~, 340. - - [507] Abstract in _J. Soc. Chem. Ind._ 1909, ~28~, 625. - - * * * * * - -The azoimide method of Dennis[508] is of interest rather than of use. He -finds that addition of potassium azoimide, N₃K, precipitates thoria -quantitatively from a neutral solution, the reaction being expressed by -the equation: - - Th(NO₃)₄ + 4N₃K + 2H₂O = 4KNO₃ + ThO₂ + 4N₃H - -Cerium, however, if present, is always precipitated with the thorium, -and cannot be removed by re-precipitation; this fact, together with the -cost of the reagent and the difficulty of obtaining it pure, renders the -method quite useless for mineral analysis. - - [508] _Zeitsch. anorg. Chem._ 1897, ~13~, 412. - -Numberless experiments have been made with organic acids in the hope -that an easy method of separation might be found, but though some useful -results have been obtained, precipitation has always to be effected in -neutral solution, so that all such processes involve the tedious -preliminary work of which an outline has been given above. Metzger[509] -finds that a quantitative separation of thorium can be effected from a -solution in 40 per cent. alcohol by use of fumaric acid; a second -precipitation is needed to secure the complete removal of the cerium -elements. Neish[510] uses meta-nitrobenzoic acid, which precipitates the -thorium salt from a boiling solution; cerium earths, if present, are -carried down in small quantities, and are removed by dissolving the -precipitate in dilute nitric acid, adding a further quantity of the -organic acid, and treating carefully with ammonia to almost complete -neutralisation. The compound obtained by this second precipitation is -the pure thorium salt. More recently, Smith and James[511] have shown -that sebacic acid gives a quantitative precipitation of the thorium -salt, from boiling neutral solution, as a voluminous granular -precipitate, readily filtered and washed; sebacic acid is very sparingly -soluble in cold water, but dissolves readily at 100°, and since, in -virtue of this property, it can be readily recovered after use, the -authors suggest it as a suitable reagent for the technical separation of -thorium from monazite. In all cases where thorium is precipitated as an -organic salt in quantitative analysis, the precipitate is dried and -ignited, and the residue weighed as the pure dioxide. - - [509] _J. Amer. Chem. Soc._ 1902, ~24~, 275 and 901. - - [510] _Ibid._ 1904, ~26~, 780. - - [511] _Ibid._ 1912, ~34~, 281. - -An interesting method has been worked out by Giles.[512] If pure moist -lead carbonate be stirred into a neutral solution of rare earth -compounds, thoria is completely precipitated. Only the tetravalent -elements are separated by this method, so that if ceric compounds are -present, they must first be reduced by means of sulphuretted hydrogen or -sulphur dioxide; zirconium, if present, must afterwards be separated -from the thorium. One precipitation is said to ensure almost complete -separation from the trivalent elements. The precipitate is collected, -washed, and dissolved in hydrochloric acid; after filtering, if -necessary, the solution is saturated with sulphuretted hydrogen, to -ensure complete removal of the lead, and thorium hydroxide is then -precipitated by ammonia. The drawback to this method lies probably in -the fact that it is necessary to use absolutely pure lead carbonate, a -substance which, as the author’s elaborate process of purification seems -to show, could not be obtained very cheaply on a large scale. - - [512] _Chem. News_, 1905, ~92~, 1 and 30. - -An account has recently been published[513] of a volumetric method for -the estimation of thorium. The mixed oxides are dissolved in -concentrated acetic acid, and the solution titrated with a standard -solution of ammonium molybdate. This reagent effects complete -precipitation of thorium, but does not react with compounds of the -cerium elements; excess of the molybdate is shown by a solution of -diphenyl carbazide, CO(NH·NH·C₆H₅)₂, used as an external indicator. The -carbazide, which is obtained by the action of phenyl hydrazine on urea, -has the property of producing definite, though evanescent, colourations -with compounds of many of the metallic elements; a drop of the working -solution, brought into contact with a drop of the carbazide solution, -shows a deep rose colouration when excess of ammonium molybdate is -present.[514] - - [513] Metzger and Zons, _J. Ind. Eng. Chem._ 1912, ~4~, 493. - - [514] Vide Skinner and Ruhemann, _Trans. Chem. Soc._ 1888, ~53~, 554; - also Cazeneuve, _Compt. rend._ 1900, ~131~, 346. - -The iodate process of Meyer and Speter[515] has the great advantage that -it is carried out in a strongly acid solution, so that here the tedious -purification from phosphoric acid is no longer necessary. After -decomposition of the mineral with sulphuric acid, the sulphates are -extracted with water, and a suitable quantity of nitric acid added; the -solution is then treated with a nitric acid solution of potassium -iodate, and the thorium iodate which separates is dissolved in -concentrated nitric acid, and re-precipitated to remove traces of the -cerium elements. The iodate, after washing, is dissolved in hydrochloric -acid, and reduced by sulphur dioxide; the hydroxide is then precipitated -by ammonia. Since zirconium is also thrown down under these conditions, -the hydroxide is dissolved in hydrochloric acid; pure thorium oxalate is -precipitated from this solution by oxalic acid, and is ignited and -weighed as oxide, in the usual manner. Since ceric iodate is also -insoluble in dilute nitric acid, it is necessary to reduce any ceric -compound which may be present before the iodate treatment by the usual -methods. - - [515] _Chem. Zeitg._ 1910, ~34~, 306. See also _Zeitsch. anorg. Chem._ - 1911, ~71~, 65. - -Another method which can be carried out in acid solution is based on the -insolubility of the hypophosphite, ThP₂O₆,11H₂O, in dilute acids.[516] -To the boiling acid solution, an aqueous solution of sodium -hypophosphate, Na₂H₂P₂O₆,6H₂O, is added drop by drop. The precipitate, -which contains any titanium and zirconium present in the original -solution, is best treated with a mixture of sulphuric and fuming nitric -acids; the phosphates produced by the oxidation are freed from nitric -acid by evaporation, dissolved in water, with addition of sulphuric -acid, and thorium precipitated as the oxalate, which is then ignited as -usual. This method has been suggested for the technical separation of -thorium from monazite (_vide_ p. 278). Since the precipitations by means -of sodium hypophosphate and potassium iodate can be carried out with -solutions obtained directly from the product of the action of sulphuric -acid on the mineral, these two methods are probably more suitable for -the rapid and accurate estimation of thorium for technical purposes than -any of the others mentioned. - - [516] Wirth, _Zeitsch. angew. Chem._ 1912, ~25~, 1678; see also Koss, - _Chem. Zeitg._ 1912, ~36~, 686, and Rosenheim, _ibid._ p. 821. - - -CHAPTER XIX - -THE MANUFACTURE OF MANTLES FROM COTTON AND RAMIE - -The fabric chosen for the manufacture of the original Welsbach mantles -was a specially selected cotton, woven from threads of a specified -thickness. The oxide skeleton left after burning off the impregnated -fabric, however, showed many serious defects. Gradual shrinkage occurred -during use, so that the mantle was gradually withdrawn from the hottest -zone of the flame; the contraction also resulted in crumpling, which -caused the fragile fabric to fall to pieces. The light-giving power -showed a gradual but continuous diminution, so that after a hundred -hours, the decrease sometimes amounted to thirty per cent. of the -original intensity. Lastly, owing to the fragility due to the torsion -introduced by the twisting together of so many short fibres in the -spinning of the fabric, the life of these mantles was very short, and -their susceptibility to shock very great. - -With the introduction of ramie, many of these defects disappeared. -Mantles made from this fibre do not shrink continuously, nor to any -considerable extent, so that crumpling does not occur; the decrease in -light-giving power is very much less than with the cotton mantles, the -life is much longer, and the resistance to shock very much greater. -Microscopic examination of the fibres, and of the ash left after burning -off, shows that these differences are traceable to differences in the -mechanical structure of the two fabrics. The cotton thread is spun from -a very large number of very short fibres, which are twisted together, -whereas the separate fibres of ramie are of much greater length, and the -torsion in the thread correspondingly less. In the case of artificial -silk, continuous filaments are spun into threads, and this simple fact -accounts for the very much greater durability and elasticity of mantles -made from this fabric. - -The introduction of ramie for the manufacture of mantles effected no -great alterations in the processes employed in the case of cotton; the -treatment of artificial silk, however, requires a profoundly modified -method, and in consequence the preparation of this fabric and the -manufacture of mantles from it, are considered separately in another -chapter. Though the manufacture of artificial silk was first commenced -in France, it is in Germany that its adaptation to the incandescent -mantle industry has been successfully effected. Its adoption, however, -has not yet become general, and by far the greatest number of mantles -are to-day made from ramie. In the United States, where the early -working of the monazite deposits gave a great impetus to the industry, -the manufacturers still cling largely to the older methods, so that even -now quite a considerable number of mantles are made from cotton. - -In the present chapter, a short account will be given of the methods -employed in the manufacture of mantles from ramie and cotton. The -general methods of preparation of cotton fabrics are well known. Ramie -is prepared from the tschuma plant, which is found in India, China, and -other parts of Asia. The fibre is obtained from the inner side of the -bark; this is dried, pressed into bales, and exported. After removal of -gum and resin, by heating with sodium hydroxide solution under pressure, -the fibre is bleached, dried and cleaned, and then combed and spun in -the usual manner.[517] - - [517] For the preparation and technical uses of Ramie, or Rhea, as it - was formerly called, _vide_ Cross, ‘The Industrial Uses of Cellulose,’ - in the _Cantor Lectures of the Society of Arts_, 1897, ~vi~, p. 20. - - -~Washing.~--The influence of even small quantities of impurities on the -intensity of the light emitted by a mantle is remarkably great, and the -manufacture requires a degree of care and attention far beyond that -needed in ordinary technical processes. Washing of the fabric in -particular must be very thorough and careful, if a mantle of reasonable -quality is required. If the mineral content of the fabric, _i.e._ the -ash left on incineration, amount to more than 0·03 per cent. of the -total weight, the quality of the mantle is seriously affected. -Particularly is this the case if even the smallest traces of iron come -in contact with the fabric; on this account wooden implements must be -used as far as possible in the washing house, and all iron parts must be -carefully protected so that no water can drip from them on to the -material. - -The fabric is used in the form of a long cylindrical tube usually of -about twice the diameter required for the base of the finished mantle. -Before the mineral impurities can be removed, this must be entirely -freed from grease. It is therefore washed thoroughly with a warm -solution of sodium carbonate, which removes all the hydrolysable fats. -If paraffin or other non-hydrolysable grease is present, the alkaline -wash must be followed by a soap wash. The fabric is now cleansed from -alkali and soap by running water, and mineral impurities are removed by -treatment with dilute hydrochloric acid (1-3 per cent.) at a temperature -of 50°-60°C.; it is finally washed free from acid with distilled water. -So susceptible is the mantle to traces of impurity that the use of -ordinary tap water, or even of a distilled water which has become -contaminated to the smallest degree, for this final washing, will -considerably lower its efficiency. - -A centrifugal machine removes most of the water, and the drying is -completed by passage over wooden rollers, through a small chamber, of -which the air is kept at 30°-40°C. The dried fabric is now cut into -lengths ready for the next process. - -[Illustration: FIG. 11] - - -~Impregnation.~--The composition of the ‘Lighting Fluid,’ as the -solution of salts used for impregnation is technically termed, varies -slightly according to the nature of the mantle required, and the -conditions of washing. It is of the greatest importance that the ratio -of thoria to ceria should be constant and definite; the usual -proportions are chosen so that the ratio of the oxides is 99 : 1. Fig. -11 shows at a glance to what a remarkable extent small variations in the -percentage of ceria affect the luminosity of the finished product.[518] -The thorium nitrate is made up with distilled water to a solution of -25-35 per cent. strength, and the calculated quantity of a standard -solution of cerium nitrate is added. It is usual to add to the mixture a -small quantity of another nitrate, which on ignition will leave an oxide -of which the function is to strengthen the skeleton of ash. Beryllium, -zirconium, magnesium, or aluminium nitrate is usually employed, in -quantity calculated to leave an amount of oxide constituting about 0·5 -per cent. of the total oxides; for ramie fabrics, beryllium nitrate is -generally chosen. - - [518] Numberless theories have been advanced to account for the - extraordinarily high light-emitting power of this particular mixture - of thoria and ceria. An account of these would be beyond the province - of the present work; the reader who desires to pursue the subject - should consult the interesting work of Dr. H. W. Fischer, _Der - Auerstrumpf_, Ahren’s _Sammlung_, 1906, vol. xi. _Vide_ also Lévy, - _L’Éclairage à l’incandescence par le gaz_, Paris, 1910, Ch. II; and - Foix, _Thèse présentée à la Faculté des Sciences de Paris_, Paris, - Gauthier-Villars, 1910. - - The diagram is after Drossbach, _J. Gasbel_. 1898, 352. - -After having been immersed for two to five minutes in the solution, the -separate lengths are freed from excess of the lighting fluid by means of -a small wringing machine. The pressure between the rollers must be -regulated very exactly, since on the amount of solution taken up by the -fabric will depend the mass of the oxide skeleton. The weight of oxides -left after ignition should be 0·5-0·6 gm. for a ‘normal’ upright mantle -of 9·5 cm. length, corresponding to 1·0-1·2 gms. of the nitrates, or, -for a 30 per cent. solution, to 3·3-4·0 gms. of solution. The weight of -the fabric before impregnation is approximately 5 gms. for cotton, 3 -gms. for ramie, and 1·5 gms. for artificial silk. A cotton -mantle-fabric, therefore, must be allowed to retain rather less, a ramie -fabric rather more, than its own weight of solution, whilst an -artificial silk fabric must take up 2-2¹⁄₂ times its own weight of the -fluid. The weight of the oxide ash left from these quantities has been -found by experience to be most suitable; if the mass is greater than -this, the light-emission is diminished without a compensating gain in -strength; if it is less, the light-emission is indeed greater, but the -mantle becomes too fragile. - -The impregnated fabric-lengths, after passing through the wringing -machine, are drawn singly on to glass forms which are arranged on -stands, and freed from moisture in a drying room by hot air, a -temperature of about 30°C. being maintained. Three to four hours are -required, under these conditions; if the drying be too rapid, -considerable shrinkage occurs, and the mantles obtained are then -extremely fragile. - - -~The Mantle Head.~--The normal upright mantle is supported from a -central rod of compressed magnesia--fused quartz has recently been -suggested[519]--by means of an asbestos thread. The thread in the older -patterns was supported by simply doubling over the fabric at the end -which was to become the head; more generally, however, a strip of tulle -or gauze is sewn to the head end before the impregnation. In order to -strengthen the head, it is treated before ‘finishing’ with a hardening -or ‘fixing’ fluid, which usually consists of a mixture of magnesium and -aluminium nitrates in aqueous solution; the following may be cited as a -typical mixture: Aluminium nitrate, 300 parts; magnesium nitrate, 300 -parts; chromium nitrate, 3 parts; borax, 5 parts; distilled water, 1500 -parts. In order to secure that this fluid is applied to the head only, a -little organic colouring matter is generally added, so that it may be -clearly seen. The solution is soaked on to the head from mechanically -held felt pads, which are kept at a convenient degree of saturation with -the fluid by means of an ingenious compressed-air device. The mantle is -then rapidly dried in a hot-air chamber. - - [519] _Vide_ _D. R. P._ 244959, March, 1912. - -After the fixing and drying processes, the head is ‘finished.’ The -ordinary upright mantle is sewn together, at the end which has been -treated, with carefully selected asbestos threads, an opening of some -ten millimetres being left, and the asbestos is threaded diametrically -across this opening--these diametrical threads support the mantle on its -rod during use. These operations were formerly done by hand, when -mantles of good quality were required, but machine treatment is -gradually coming into extended use. Several mantles now on the market -are supported at the head by metal rings, made from thin sheets of iron -which have been plated with aluminium. In petroleum lamps, the mantle is -usually supported from both sides by means of asbestos threads. - -In the case of fabrics from which ‘inverted’ mantles are to be made, -fixing is carried out as usual at one end, to a depth of about 1·5 cm. -After drying, a strip of about 0·5 cm. width is bent over and sewn down, -and through this double band an asbestos thread is drawn, by which the -mantle is secured to a magnesia ring. The lower end is drawn together in -the shape of a hemisphere, by means of threads drawn through the meshes -of the fabric; an opening of 6-8 mm. is sometimes left, but in the more -modern patterns the end is drawn almost completely together, and after -cutting is pressed out on a wooden shaper by a wooden mallet. - -The product is now ready for burning off; if it is to be marked, it is -stamped at this stage with a solution of didymium nitrate and methylene -blue; the former being only faintly coloured, the organic dye is added -to give a definite impression. On ignition, the nitrate is converted -into the oxide, which is deeply coloured, and, of course, permanent. - - -~Burning off and Shaping.~--For the production of mantles of the best -quality, these processes are usually carried out by skilled operators, -each mantle being treated separately. Very frequently, however, -mechanical arrangements are employed. The great objection to machine -treatment of such a product lies in the fact that it must be identical -for every mantle; whereas it is exceedingly difficult to ensure that the -original fabric, and the processes of washing, impregnating, wringing, -and drying have been absolutely uniform. The operation of shaping and -hardening is a very delicate one, and on the care with which it is -carried out, the quality of the mantle finally depends. Until quite -recently, only the cheaper kinds of mantles were machine-treated; but as -the uniformity of the fabric becomes more assured, and the earlier -operations more exact, employment of machines at this stage will -undoubtedly increase. - -The prepared fabric is shaped on a suitable form, and removed by a -holder, which supports it from the asbestos thread; a flame is then -applied to the head. The burning-off proceeds readily, once started; -when the upper half has been incinerated, the flame is removed. The -weight of the unburnt portion prevents too rapid contraction taking -place at first; when the flame is removed, the glow spreads slowly -downwards, and the shrinking is thus kept as uniform as possible. The -operation must be carried out under a ventilating hood. The organic -material of the fabric is completely oxidised, and the nitrates are -converted into oxides, which retain the exact shape of the original -fibres. The skeleton now undergoes the process of shaping and hardening, -for which a ‘radial’ blowpipe flame is used. The burnt-off product is -placed over this; the gas is supplied at an initial pressure of only a -few inches of water, which is increased towards the end of the -operation. The process commences at the head, the mantle being slowly -lifted and rotated so that it is shaped and hardened along the whole -length. By this means the oxide skeleton is not only suitably shaped, -but is rendered considerably more elastic and resistant. For inverted -mantles, of course, specially shaped burners are required. The eyes of -the operators must be protected from the glare by shades of green glass. -Recently the processes of burning-off and hardening have been carried -out by means of the same burner. - -Where machines are employed, the prepared fabrics are burnt off on wire -shapers, usually in rows of ten; mechanical arrangements for continuous -ignition and motion and, in the hardening, for continuous elevation of -the ash-skeleton, are in use, but the finished mantles maintain a -uniform good quality only when the structure of the fabric and the -earlier processes have been absolutely uniform. - - -~Collodinisation.~--The burnt-off mantle is now ready for use, but is -far too fragile for transport. A method has therefore to be found by -which the finished product can be protected for a time without detriment -to its use for illumination. Mantles of artificial silk, particularly -those for use in high-pressure lamps, are sometimes sent out without -having undergone the final processes of burning off and shaping, which, -in this case, must be carried out on the consumer’s burner. ‘Inverted’ -mantles also were formerly sent out after impregnation and drying. In -this condition, of course, the mantles are readily packed and -transported, and there is the additional advantage that the duty on the -unburnt product is very much less than that on the finished mantle. - -One of the earliest of Auer’s patents (_vide supra_, p. 271) protected -the process of collodinisation, which is now extensively employed. The -oxide skeleton is dipped into a solution of collodion (the mixed lower -nitro-derivatives of cellulose, or cellulose nitrates) in a mixture of -alcohol and ether, to which, to prevent shrinkage on drying, a little -camphor is added. On account of the inflammability of the mixture, the -ethyl alcohol and ether are occasionally replaced by a mixture of methyl -alcohol and acetone, but with this less volatile mixture, drying of -course is slower. After dipping, the solvents are removed in a current -of air, leaving the mantle coated with an exceedingly thin film of -collodion, which increases enormously its power of resisting shock and -vibration. This film is not removed until the mantle is placed on the -consumer’s burner, when on the application of a match it ignites -instantly and burns away, leaving the oxide skeleton in the condition to -which it was brought in the final stage of hardening and shaping in the -factory. The process is now used for almost all kinds of mantles, having -been successfully applied in Germany in recent years to those made from -artificial silk. The addition of small quantities of various inorganic -salts, _e.g._ nitrates of zirconium, magnesium, platinum, thorium, etc., -to the collodion solution, has been proposed; these salts make the -collodinised product extremely resistant, but have a very harmful effect -on the oxide ash when the collodion has been burnt off. - -The collodinised mantles are cut to length on a trimming machine, and -are then ready for packing. - - * * * * * - -The present chapter may be concluded with a bare mention of a few -disconnected details, selected from the great mass of proposals, -suggestions, and developments which have sprung up round the -incandescent mantle industry.[520] - - [520] For a complete account of the mechanical developments, the - reader is referred to the monograph ‘Beleuchtung und Lichtmessung,’ by - Dr. Börnstein, in Dammer’s _Chemische Technologie der Neuzeit_, - Stuttgart, 1910-11, ii. 243-266. - -With regard to the composition of mantles, numerous proposals have been -made. It is stated that thoria with 0·25 per cent. of uranic oxide, UO₃, -gives a light almost equal to that of the Auer mantle. Zirconia with -0·40 per cent. of vanadium, in the form of the pentoxide, is said to -give a splendid white light; the vanadium oxide slowly volatilises, but -addition of an equivalent proportion of silica is said to prevent this. -Langhans claims to have obtained a product equal in light-giving power -to the Auer mantle, by using as impregnating fluid a solution of -colloidal silica, obtained by the addition of nitric acid to a solution -of sodium silicate, to which suitable quantities of rare earth nitrates -are added. Bodies obtained by the use of very similar solutions give -skeletons which are coming into extended employment for gas radiators. -The ‘Sunlight’ mantles use a mixture of thoria (50 per cent.), alumina -(40 per cent.), and chromium sesquioxide (10 per cent.). - -A direction of development in which some success has been attained is -the introduction of self-lighting devices. The catalytic action of -finely divided metals has been proposed in innumerable patents,[521] but -these devices are unreliable, and it seems doubtful if chemical methods -will ever be successfully applied to the problem. For the lighting of -streets, shops, etc., the ‘by-pass’ system is employed; a tiny jet of -gas burns continuously from a pin-hole nozzle, which is momentarily -increased, when the main supply is turned on, to such an extent that the -gas issuing from the burner is ignited.[522] - - [521] _Vide_, _e.g._ _D. R. P._ 158974 and 253550; _F._ 417934. - - [522] For automatic regulators for self-lighting, _vide_ _J. Gasbel_. - 1910, ~53~, 490. - -An account of the innumerable forms of lamps and burners which have been -introduced in the last twenty years would fill several volumes. The -theoretical grounds on which improvements in this direction are based -are outlined in an able article by Dr. H. Bunte, a recognised authority -on incandescent lighting, which appeared recently;[523] for an account -of some of the lamps which have been successfully applied, the reader is -referred to a recent French publication.[524] - - [523] _J. Gasbel._ 1911, ~54~, 469; _vide_ also Pickering, _J. - Gaslighting_, 1911, ~113~, 156. - - [524] _L’Éclairage à l’incandescence par le gaz_, Lévy, Part I. Ch. - III. - - -CHAPTER XX - -ARTIFICIAL SILK--ITS PRODUCTION AND USE IN THE MANTLE INDUSTRY - -The history of the artificial silk industry, since its foundation about -the year 1890, illustrates curiously the rapidity with which isolated -facts, of apparently merely academic interest, are seized upon and -adapted to the needs of modern civilisation. It is during this period, -especially, that the bonds between science and industry, in a dozen -different directions, have been drawn so close that to-day it is in many -cases impossible to differentiate the two. The pure science of to-day is -the technology of to-morrow--and not always even of to-morrow, but of -to-day. But we have moved even beyond this; the industrial needs of the -day are creating and extending our science at a rate which shows how -relatively poor a stimulus has been the mere desire for knowledge. Such -has been the history of the artificial silk industry. No sooner had -Chardonnet shown that the preparation of a new fabric was not only -possible but profitable, than a thousand aspects of the problem were -taken up. Patents were taken out on all sides--the majority, as usual, -valueless, one or two of great importance. Companies were formed, -factories built, machines invented; numberless applications were -proposed, mostly again worthless, whilst patient research and -innumerable experiments have carried one or two suggestions to a -successful place in practice. Among these has been the adaptation of -artificial silk to the manufacture of mantles, which will be outlined in -the present chapter. Before taking up this question, however, a short -account of the manufacture of the fabric itself must be given. - - -~Chardonnet Process.~--In the Chardonnet process, an account of which -was published about 1890, continuous fibres are obtained by forcing -through tiny jets a viscous solution of collodion, or nitrocellulose, as -it has been misnamed, in a mixture of ethyl alcohol and ether. In the -original form of the process, the solution was forced into water, which, -by removing the alcohol and ether, caused an instantaneous coagulation -of the surface, so that a filament was obtained which could be wound -directly on to a spool. More generally, however, the jets deliver the -solution into a chamber through which warm air is passed; this is -equally effective in removing the solvents and causing surface -coagulation, and the filaments are woven directly into threads of ten to -forty strands, according to the purpose for which the fabric is -required, fifteen to twenty being used for silk from which mantles are -to be made. On account of its inflammability, the thread is denitrated -by means of a solution of ammonium sulphide. - -The raw material for the process is cellulose, usually in the form of -cotton. Treatment of this with a suitable mixture of concentrated -sulphuric and nitric acids replaces some of the hydroxyl groups by the -‘nitrate radicle,’ NO₃, a mixture of various nitrates of cellulose being -formed, in which the so-called tetra-, penta-, and hexa-nitrates -predominate.[525] The product, cellulose nitrate or collodion, very -closely resembles the original cellulose in appearance and structure. It -is washed thoroughly to free it from traces of acid--which render it -liable to explode spontaneously--and after drying, dissolved in the -minimum quantity of the mixed solvents;[526] the solution is filtered -from insoluble impurities through wads of cotton, pressures of thirty to -sixty atmospheres being required. This filtration purifies and -thoroughly mixes the solution, so that perfect uniformity is obtained in -the product. The glass jets through which the solution is now forced, -under a pressure of forty to fifty atmospheres, have a diameter of 0·08 -mm., but the threads obtained contract on the removal of the solvents, -so that fibres of 0·01-0·02 mm. are formed. - - [525] The cellulose esters are usually named as if they were derived - from a compound C₁₂H₂₀O₁₀, the formula for cellulose being - (C₆H₁₀O₅)_{_n_}. Thus the formation of the ‘hexa-nitrate’ would be - represented-- - - C₁₂H₂₀O₁₀ + 6HNO₃ = C₁₂H₁₄O₄(NO₃)₆ + 6H₂O. - - [526] In the Lehner process, in which collodion is also used, larger - quantities of solvent are employed, so that much more dilute solutions - are obtained; these require low pressures to form the thread, which is - then hardened chemically. - -Chardonnet probably began his work about 1885. It is interesting to -observe that an Englishman, Swan, had proposed in 1883 to use a solution -of collodion in acetic acid, fabrics prepared by his process being shown -at the London Exhibition of 1884.[527] - - [527] _Vide_ Böhm, _Zeitsch. angew. Chem._ 1912, ~25~, 657. There is - no account of this process in the English patent literature. - - -~The Pauly or Cuprammonium Process.~[528]--It has long been known that a -solution of copper hydroxide in ammonia solution--Schweitzer’s -reagent--will dissolve cellulose. The use of this solvent for the -production of artificial silk was proposed about 1900, and the method -has become a serious rival of the older Chardonnet process. The solvent -is prepared on a large scale by passing air through an ammonia solution -to which copper turnings have been added. After addition of the -cellulose, and filtration, the solution is forced through tiny jets into -a bath of dilute acid, which removes the copper and precipitates the -cellulose again. - - [528] A full account of this and of the other processes employed in - the manufacture of artificial silk will be found in the work of Piest, - _Die Zellulose_, Stuttgart, 1910. - -The solution of cellulose by Schweitzer’s reagent is undoubtedly a -chemical action. Cellulose is to be regarded as a polyhydric alcohol, -with one or several atoms of hydrogen of the hydroxyl groups replaceable -by metals. According to Piest (_loc. cit._) a ‘Cupramine base’ is formed -by the replacement of this hydrogen by copper and the amino-group, NH₂. -The action of sodium hydroxide on cellulose, however, is generally -regarded rather as an additive reaction, the product, ‘alkali -cellulose,’ being usually written C₆H₁₀O₅,NaOH. A careful chemical -investigation alone can reveal the actual nature of the compound formed; -such an investigation, apart from its scientific interest, might yield -results of considerable technical importance. - - -~The Viscose Process.~--Shortly after the introduction of the Chardonnet -process, patents were taken out which protected a very cheap and simple -method of dissolving cellulose,[529] which had been discovered by two -well-known English authorities. Cross and Bevan. They found that -mercerisation, _i.e._ the action of the sodium hydroxide on cellulose, -produces a swollen, transparent mass, which very readily takes up carbon -disulphide. When exposed to the action of this liquid for three or four -hours, at ordinary temperatures, the mass swells further, gelatinising -and becoming soluble in water. On treatment with water, a yellowish, -extremely slimy solution is obtained, from which cellulose is -precipitated on prolonged standing, by heating, or by oxidation. The -substance is apparently a cellulose xanthate, and may be written -NaS·CS·O·C₆H₉O₄,NaOH.[530] On account of the extremely viscous nature of -the aqueous solution, Cross and Bevan gave it the name Viscoid. - - [529] _Vide_, _e.g._ Cross, Bevan, and Beadle, _D. R. P._ 70999, - granted September, 1893. - - [530] _Vide_ Beltzer, _Zeitsch. angew. Chem._ 1908, ~21~, 1731. - -During the last few years this method of dissolving cellulose has been -employed in the manufacture of artificial silk, under the name ‘Viscose -Process.’ The product obtained is very suitable for the manufacture of -incandescent mantles, and is considerably cheaper than either the -Chardonnet or Pauly silk. - - -~The Acetate Process.~--Quite recently numerous experiments have been -carried out with the object of finding methods for employing the -cellulose esters of organic acids in the preparation of fabrics. The -acetate, which is generally used, gives solutions from which fibres can -be obtained which are comparable to natural silk in strength, and which -have the further advantage of being non-inflammable, and far less -readily affected by water than artificial fabrics obtained by the above -methods. It is prepared by treating cellulose with dilute acid, by which -the so-called ‘hydrocellulose’ is obtained; this is treated with a -mixture of glacial acetic acid and acetyl chloride, and the whole, after -addition of a little concentrated sulphuric acid, warmed to 65°-70°C. -As early as 1894, Cross and Bevan[531] had patented a process for this -preparation by the action of acetyl chloride in the cold on an intimate -mixture of cellulose and zinc chloride. - - [531] _E._ 9676, 1894. - -From the solution obtained, the acetates are precipitated by water, -washed and dried. The mixture of esters dissolves in chloroform, -nitromethane, acetic acid, phenol, pyridine, etc., and is -re-precipitated by addition of alcohol, benzene, or ligroin (petroleum -ether). On account of its non-inflammable character, cellulose acetate, -as the product is called, is being used instead of the nitrate in the -manufacture of celluloid; it is also used for non-inflammable -cinematograph films. Fibres can be obtained by forcing the solutions -through jets, and removing the solvent, as in the above processes; these -are spun into threads which are coming into increasing use, on account -of their extremely low conducting power, for the insulation of very fine -electric leads. The product is at present too expensive, however, for -use in the textile industries, or for the manufacture of mantles. - -A solvent which had at one time some technical importance is zinc -chloride.[532] The concentrated aqueous solution of the salt will take -up cellulose in considerable quantity; and the solution has been used in -the preparation of carbon filaments for glow lamps. - - [532] Gulbrandsen, _Prog. Age_, 1912, ~30~, 77; Wynne and Powell, _E._ - 16805, December, 1884. - -The fabrics prepared by the processes which have been mentioned above -are of great technical value. In lustre they far surpass natural silk, -and they take dyes very well, but owing to the ease with which they -tear, they cannot be woven alone for textiles, but are always used in -‘mixed’ materials. The acetate silk, which approaches the natural fibre -in strength, is not much less expensive. Whilst the price of natural -silk is roughly 35 francs per kilo. (approx. 13_s._ 3_d._ per lb.), the -costs of production of the artificial fabrics are--Chardonnet 15 frs., -Pauly 12 frs., Viscose 7 frs. per kilo. (respectively 5_s._ 8_d._, 4_s._ -6_d._, and 2_s._ 8_d._ per lb.). Artificial silk, however, has uses -distinct from the natural fibre, and is at present a competitor with it -in one or two small fields only. Thus the production of natural silk is -ten times that of artificial silk (50,000,000 kilos. per annum to -5,000,000 kilos.) in spite of the difference in price. - -Artificial silk is very susceptible to the action of water, which -weakens it very considerably. Its resistance is said to be greatly -increased by the action of formaldehyde; the fabric is plunged into a -bath containing an aqueous solution of the aldehyde, to which a little -lactic acid has been added. The chemistry of the change is discussed at -length by Beltzer (_loc. cit._). - -The threads of artificial silk far surpass in lightness those spun from -vegetable fibres. A thread of twenty strands weighing one pound -avoirdupois would be more than twenty miles long. At the same time the -filaments have not the irregular tubular structure of vegetable fibres, -but are solid cylinders. The fact that the filaments are continuous, so -that there is relatively little torsion in threads spun from them, gives -artificial silk its great advantage over the natural vegetable fibres -for the manufacture of mantles. For this purpose the Pauly or -Cuprammonium silk is most suitable, though Viscose silk is almost as -good; the fibre obtained by the Chardonnet process is not quite so -useful in this direction. - - -~The Manufacture of Mantles from Artificial Silk.~--Whilst the fabrics -made by the various processes outlined above are more expensive than the -cotton and ramie formerly exclusively used in the mantle industry, they -have the advantage, in addition to the fact that they produce better and -more lasting mantles, that they do not need the laborious and -troublesome process of washing which is so essential in the case of the -vegetable fibres. From the nature of the methods used in its -manufacture, artificial silk can contain no mineral residue; hence the -fabric is immediately ready for impregnation. - -As early as the year 1892 Schlumberger and Sinibaldi proposed the use of -Chardonnet silk for the manufacture of mantles; but their patent, a -Belgian one,[533] attracted little attention, although they stated -clearly that the denitrated silk will readily take up the lighting -fluid. Ignorance of this fact deferred the successful application of -this fibre for ten years. In 1894 De Mare suggested the preparation of -mantles by addition of the necessary salts to the collodion solution -before squirting; in the following year Knöfler used the same process, -recommending in addition the use of ammonium sulphide to denitrate the -impregnated threads. These two attempts, which were found to be -unworkable, owing to the difficulty of obtaining a homogeneous product -before squirting, were merely efforts to compete against the Auer -monopoly, resting on Welsbach’s patents, which covered impregnation of -any natural fibre. In Knöfler’s process,[534] the salts were dissolved -in alcohol and added to the collodion solution, which was then forced -through jets into water, to which ammonia was added to prevent removal -of the nitrates in solution; the threads were then denitrated with -ammonium sulphide. The ammonia treatment of course converts the nitrates -into the insoluble hydroxides, a departure which was followed in most of -the numerous patents inspired by Knöfler’s process. - - [533] _Vide_ Böhm, _Zeitsch. angew. Chem._ 1912, ~25~, 657. Apparently - this patent was not taken up; no account of it has been found in the - published patents of the Belgian Government. - - [534] _E._ 11038, 1895, granted July, 1895. - -The first indications of the method which ultimately led to success are -to be found in a patent taken out by Plaisetty, in 1901.[535] The -specification protects the addition of thorium and cerium hydroxides to -the cuprammonium solution of cellulose, but apparently without any -inkling of the results that were to follow, and more or less -incidentally, he includes in this patent the impregnation of the -finished fabric and the subsequent treatment with ammonia. In the -following year he applied for a German patent,[536] which was granted in -May, 1903, in which he definitely protects the impregnation of the -finished fabric, and the ammonia treatment, the fabric being then washed -and dried, and burnt off as usual. - - [535] _E._ 20747, 1901. - - [536] _D. R. P._ 141244. - - -~Impregnation.~--Since the filaments from which artificial silk is -obtained are solid and rod-like in form, as opposed to the tubular -structure of cotton and ramie filaments, it is rather surprising that -the fabric should take up the lighting fluid in the necessary quantity -(_vide_ p. 295). It is found that a 50 per cent. solution of nitrates -gives the best results, the impregnation requiring half an hour; a warm -bath is usually employed. It is usual to add to the bath a quantity of -thorium hydroxide, since the thorium nitrate of commerce generally -contains nitric acid, which has a bad effect on the fabric.[537] The -excess of solution is removed by means of a glass or porcelain -centrifuge, not, as with cotton or ramie mantles, by use of a wringer; -drying must be carried out very slowly. The fabric is not cut into -lengths before impregnation, as in the case of cotton or ramie, but is -immersed in the lighting fluid in long strips. - - [537] _Vide_ Buhlmann, _D. R. P._ 188427, 1907; also _E._ 6828, 1907. - - -~‘Fixing.’~--If the dried fabric, impregnated with the necessary salts, -be finished and burnt off in the usual way, the oxide skeleton is -extremely fragile, and soon falls to powder. The reason for this lies -probably in the explosive decomposition of the nitrates, the weight of -organic matter relative to the salts being very much less than in the -case of ramie or cotton fabrics (_vide_ p. 295). The additional ammonia -bath advocated by Knöfler (_vide supra_) was therefore adopted by -Plaisetty, and the nitrates in the dried impregnated fabric are -converted into hydroxides by this treatment. For this process, to which -the name ‘Fixing’ has been given by Böhm, numberless alternative -proposals have been made. Plaisetty’s ammonia fixing gives a mantle -which, after burning off, is exceedingly elastic and strong, but it is -nevertheless open to serious objections. Thus the nitrates may be to -some extent dissolved out by the fixing bath before precipitation of the -hydroxides has occurred; to remedy this, the impregnated fabric must be -very thoroughly dried before fixing, and in this case, apart from the -trouble involved, the acid of the commercial nitrates will attack the -fabric unless addition of thorium hydroxide has been made to the -impregnating fluid. Again, the conversion into oxides is not complete, -the outer layer first formed preventing free diffusion of the alkaline -fluid. Finally, since ammonium nitrate is formed in the reaction, a very -thorough washing is necessary to remove this salt. - -It would be impossible to mention all of the numberless proposals which -have been put forward for fixing; nor are the great majority worthy of -mention.[538] One of the most important was that of Albrecht,[539] by -which hydrogen peroxide is substituted for ammonia. This reagent, as is -well known, precipitates from solutions of thorium salts ‘peroxide’ -compounds (_vide_ p. 255); from the fabric impregnated with the nitrate, -free nitric acid is liberated in the reaction. Since the peroxide is -soluble in nitric acid, two baths are used, the fabric being allowed to -remain for a short time only in the first, which becomes strongly acid, -and being then transferred to the second, in which the precipitation is -completed. The burning off of the product so treated proceeds quite -quietly, and leaves a very hard and elastic skeleton. The method, -however, has the grave disadvantage that cerium salts are not -precipitated under these conditions, but escape into the solution. To -remedy this, arbitrary additions of cerium nitrate are made to the -fixing bath, but the percentage of cerium, and therefore the lighting -power (_vide_ p. 293) of mantles fixed by this method is liable to -fluctuate. A modification has been introduced[540] in which various -salts are added to the hydrogen peroxide fixing baths to prevent the -withdrawal of the cerium salt; these are chiefly acetates of the alkali -metals and allied compounds. The fabric requires washing after this -treatment. - - [538] A large number of patents are mentioned by Böhm, _J. Gasbel._ - 1909, ~52~, 855. - - [539] _D. R. P._ 188427, September, 1907; _E._ 15295, 1907. - - [540] _Vide_ _E._ 2240, 1908. Cerofirm Gesellschaft, by Brit. Cerofirm - Co. - -A rather similar proposal[541] substitutes for ammonia an alkaline -solution of hydrogen peroxide, obtained by dissolving sodium peroxide in -water. After saturation for a minute or so, the fabric is wrung out and -dried, there being no necessity, according to the patent, for any -subsequent washing. The same company in an earlier patent[542] suggest a -fixing bath of ‘an alkali or amine with an acid which can form insoluble -basic double salts with the earth metals,’ the said salt to be -precipitated on the fibre, whilst an alkali or amine nitrate goes into -solution; acetic and benzoic acids and phenol are mentioned. Apparently -this process did not give satisfactory results. The same may be said of -the hypochlorite method of Visseaux.[543] Equally interesting, and -doubtless equally practical is the proposal[544] to treat the dried -impregnated mantle with ozone in a closed chamber, which possibly -inspired the even more original suggestion[545] that the fabric be first -washed in ozonised water, dried, then impregnated and dried, and finally -treated with ozone. According to yet another French patent,[546] the -impregnated and dried fabric is to be treated with an alcoholic solution -of hydrofluoric acid, which will give a viscous insoluble mixture of -thorium and cerium fluorides in the fabric, and at the same time will -remove any impurities. Another patent[547] proposes the use of hydrazine -and similar bases, cerium nitrate being added to the fixing solution. - - [541] _D._ 247940, June, 1912; _F._ 430417, August, 1911. - - [542] _F._ 403433, September, 1909, Bruno Co. - - [543] _F._ 408807, February, 1910. - - [544] _F._ 414700, June, 1910. - - [545] _F._ 422643, January, 1911. - - [546] _F._ 426156, April, 1911. - - [547] _E._ 11904, 1909. - -Innumerable suggestions have been made for fixing by means of ammonia -gas, or vapours of organic bases.[548] An English patent granted in -February 1910[549] protects ‘various improvements,’ which consist in -carrying out a preliminary treatment with steam, impregnation with the -solution of nitrates, conversion of nitrates into oxides either by steam -carrying ammonia, pyridine, etc., or by the action of these vapours -without steam in a vacuum, all in one chamber, which can be exhausted or -filled with various solutions or vapours as required. - - [548] _Vide_, _e.g._ _D. R. P._ 199615 of June, 1908. - - [549] _E._ 25549, 1908. - -More recently, the use of organic salts of thorium and cerium for -impregnation has been proposed by Dr. F. W. Wirth;[550] in fixing the -impregnated fabric with hydrogen peroxide, the cerium is not removed in -solution, since the weak organic acid formed will not dissolve cerium -peroxide. The same author has also suggested[551] the addition to the -fixing bath of substances which absorb oxygen from the air--_e.g._ -sodium hydrogen sulphite, resorcinol, tannin--to prevent removal of -cerium. He has also advocated impregnation with amorphous salts,[552] -which will obviate the necessity for any subsequent fixing treatment, -the hypophosphites and double compounds with ammonium oxalate being -specified. Attempts have been made to achieve the same end by other -methods. Thus Silbermann[553] has proposed a preliminary treatment with -alkalies (mercerisation); the fabric is treated with concentrated sodium -hydroxide solution in absence of air for half an hour, pressed through -rollers, and plunged into the impregnating solution. Two years -previously a patent was taken out by Drossbach[554] to protect the use -of colloidal solutions of the hydroxides. To a boiling suspension of -well-washed, freshly-precipitated thorium hydroxide, a solution of a -small quantity of the nitrate is gradually added; after half an hour a -colloidal solution is obtained, which, after the addition of the -required quantity of cerium nitrate, and dilution to a suitable extent, -is employed directly for impregnation. The patent states that this -solution is more readily absorbed than the ordinary nitrate solution, -but the statement has been questioned. - - [550] _Chem. Zeitg._ 1911, ~35~, 752. - - [551] _Zeitsch. angew. Chem._ 1912, ~25~, 922. - - [552] _Chem. Zeitg._ 1911, ~35~, 752. - - [553] _Chem. Zeitg._ 1911, ~35~, 1037. - - [554] _D. R. P._ 212842, August, 1909; _vide_ also Kreidl and Heller, - _E._ 17862, 1909, and _D. R. P._ 228203, 1910. - -Artificial silk itself is of a colloidal nature, the solidification of -the filaments of cellulose during the manufacture being rather in the -nature of a coagulation than of a precipitation; it is to this fact that -the fibres owe their solid, rod-like structure, and it is probably this -circumstance also which determines the very intimate absorption of the -hydroxides or peroxides produced by fixing. It is well known that -colloidal substances under some circumstances possess the property of -clinging tenaciously to foreign bodies, exhibiting the so-called -phenomenon of adsorption. The strength and elasticity of the oxide -skeleton, obtained when the fixed and dried fabric is subjected to the -operation of burning off, are presumably to be referred to such a -relation between the cellulose of the fibres and the insoluble thorium -and cerium compounds, precipitated by one of the methods of fixing -described. - - -~The Final Stages.~--The treatment of the fabric after impregnation and -fixing differs only slightly from that used for the impregnated ramie -and cotton products. The dried strips are cut into suitable lengths, and -the head is drawn together with asbestos and threaded across. No tulle -or gauze is required, the end being simply turned down before threading. -After the ordinary strengthening process for the head (_vide_ p. 296) -the process of manufacture was, until recently, finished, the goods -being sent out in the unburnt condition, on account of the difficulties -of collodinisation. These have now been overcome, so that the mantles -are burnt off and collodinised as usual. Burning off and shaping are now -frequently effected in one operation by machine; the nature of the -methods by which the fibre is made produces a uniform fabric, and if the -earlier processes are carefully carried out, a uniform product is -obtained, which is therefore suitable for machine treatment. - - -CHAPTER XXI - -OTHER TECHNOLOGICAL USES OF THE CERIUM AND YTTRIUM ELEMENTS, ZIRCONIUM -AND THORIUM - -The technical uses of the members of this group of the elements we are -considering, apart from the employment in the manufacture of -incandescent mantles, are at present very restricted. Innumerable -proposals for the employment of the compounds of cerium and the allied -metals, which are obtained in such large quantities as by-products in -the thorium industry, have been put forward, but the actual extent to -which they are utilised is so small that only an insignificant fraction -of the available quantities is annually required. In the metallic form, -a limited application is found for various alloys, _e.g._ the so-called -pyrophoric alloys, misch metal, and the magnesium and aluminium alloys. -Various compounds of the elements, as well as some alloys, have been -suggested for use in arc-lamp electrodes, and the use of the metals -themselves, as well as of various salts, for the manufacture of -flashlight powders, is protected by several patents. Investigations have -been made to determine the value of the oxides and sulphates as -catalysts in the contact process for the manufacture of sulphuric acid, -and one patent states that the yield obtained is equal to that given by -platinised asbestos. Cerium salts have been proposed for tanning, and in -the preparation of enamels; cerium sodium sulphate is used in the -catalytic oxidation of aniline to aniline black. The oxalate has a very -slight use in medicine. The oxidising power of ceric salts is of some -use in photography; ceric sulphate in acid solution is also said to be -an efficient oxidising agent for aromatic hydrocarbons. On account of -the deep colour of the higher oxide of praseodymium, didymium salts -find a limited application for marking textiles. - -Compounds of the yttrium group have at present no technical importance. -They were formerly used to some extent for the manufacture of filaments -for Nernst lamps, but with the introduction of metal filament lamps in -electric lighting, the demand for Nernst lamps and consequently for the -yttria oxides, has to a very great extent died away. - -Zirconium and its compounds, on the other hand, promise to become of -some technical importance. The metal received considerable attention in -the earlier stages of experimental work on metallic filaments for -electric lighting, but it has been shown that its melting-point is not -sufficiently high to allow of extended use in this direction. The -carbide has been proposed for the same purpose, but is even less -suitable; this compound, however, on account of its great hardness, is -likely to find employment as an abrasive, and in glass-cutting. The -oxide, which occurs in nature in an impure form as the mineral -Baddeleyite (_q.v._), is employed in the manufacture of ‘Siloxide’ glass -and of enamels, as a pigment and polishing agent, and in various forms -of lamps, _e.g._ the Nernst and Bleriot lamps, the Drummond light, etc. -Far more important, however, is its use for fire-resistant crucibles, -furnace linings and supports, etc., for which its refractory nature -renders it particularly suitable. On account of its high specific -gravity and non-poisonous character, it has been proposed for use in the -Röntgen ray examination of the human body. Quite recently, metallic -zirconium has been employed in metallurgy; addition of small quantities, -in the form of suitable alloys, is said to secure sound castings, with -increased strength and resistance to acids. - - -THE CERIUM GROUP - - -~Pyrophoric Alloys.~--It has long been known that the metals of the -cerium group possess the property, when scratched or struck, of throwing -off glowing particles; this power of emitting sparks is not lost when -the metals are alloyed, so long as the percentage of foreign metal is -not allowed to become too high. In a patent[555] protecting the use of -various ‘pyrophoric alloys,’ as these spark-giving alloys are called, -Auer states that the pure metals do not show this property, which only -appears when foreign metals are present; he accordingly patents alloys -of the cerium metals with iron, specifying particularly the alloy with -30 per cent. of the latter element. Auer’s statement has been -contradicted,[556] and it seems to be generally accepted that -misch-metal[557] of ordinary technical purity has the property of -sparking when scratched. This alloy of the cerium metals, however, is -far too soft to be useful for the purpose, and the addition of some -foreign element is required to obtain the strength, hardness, and -brittleness necessary in the various forms of ‘lighters.’ Besides the -addition of iron, the use of tin, lead, zinc, cadmium, silicon, etc., -has been patented.[558] - - [555] _E._ 16853, 1903; _D. R. P._ 154807. - - [556] _Vide_ Böhm, _Chem. Zeitg._ 1910, ~34~, 361. - - [557] The crude mixture of cerium, lanthanum, neodymium, praseodymium, - samarium, etc., with small quantities of iron and other metals, - obtained by reduction of the earth-compounds formed as by-products in - the thorium industry, is technically known as ‘misch-metal.’ - - [558] _F._ 439058, March, 1912. - -Various forms of these lighting devices are manufactured;[559] in all of -these the sparks produced by scratching the pyrophoric alloy with -hardened steel, by means of some simple mechanical device, is caused to -ignite a fragment of tinder, or a wick supplied with a suitable liquid, -_e.g._ methyl alcohol, benzene, or petrol. In the numberless forms of -cigarette-lighters at present before a somewhat indifferent public, the -friction is obtained by means of a toothed wheel, actuated by a spring -which is released when the device is opened. Many forms of gas lighter -are also on the market, but the demand for them is very small. Many -attempts have been made to adapt the device to the ignition of the Davy -miners’ lamp, but none have been successful, since it is impossible to -prevent the sparks flying through the gauze. Much work has also been -spent in efforts to utilise the pyrophoric alloys for the automatic -ignition of incandescent gas-lamps, but these have been equally -unsuccessful, so that it may be said that important technical -applications of this interesting property have still to be made. - - [559] _Vide_ Böhm, _Chem. Zeitg._ 1910, ~34~, 377; also Kellermann, - _Die Ceritmetalle und ihre pyrophoren Legierungen_, Wilhelm Knapp, - Halle, 1912, pp. 94 _et seq._ - -Auer prepared his alloys by addition of iron, or other heavy metal, to -the fused mixture of cerium metals obtained in the electrolytic -apparatus employed for the production of the latter. They can, however, -be prepared by fusing together the required quantities of foreign metal -and misch-metal, the latter being obtained by processes other than those -of electrolysis usually employed. The rare metals were obtained by the -earlier chemists in a very impure state by reduction of the halogen or -double halogen compounds with sodium or potassium. More recently[560] -much purer products have been obtained--especially in the case of -zirconium--by the action of metallic calcium, in the form of powder, on -the oxides. Another method,[561] which has been employed in the -preparation of metallic filaments for lamps, consists in heating the -oxides with powdered magnesium in an atmosphere of hydrogen or nitrogen; -by this means, hydrides or nitrides are obtained, which on heating -decompose into the gas and the metal. - - [560] _Vide_ Kuzel and Wedekind, _E._ 23215, 1909. - - [561] _Electrodon Gesellschaft_, _D. R. P._ 154691, September, 1904. - -The ease with which misch-metal and its alloys with iron and other -elements throw off glowing particles when struck is due to the low -ignition temperature of cerium, and the energy with which it combines -with oxygen. When such alloys are scratched, small fragments are struck -off, which are raised to the ignition temperature by the heat of -friction. It is generally accepted, however, that this explanation is by -no means a complete one, and the existence of a pyrophoric suboxide was -suggested.[562] The theory was advanced that the pyrophoric properties -of the alloys were due primarily to the formation on the surface of a -film of this sub-oxide, and the partial oxidation of cerium alloys, -protected by patent (_loc. cit._), was said to cause a marked increase -in the ease with which sparks could be obtained. In this connection, an -experiment of Hirsch, who has thoroughly investigated the properties of -metallic cerium,[563] is of interest. He found that when the element is -warmed in a sealed glass bottle, a black powder forms on the surface, -which, when the bottle is opened, ignites spontaneously. It is probable -that this black sub-oxide plays an important part in the production of -sparks from the ordinary pyrophoric alloys. - - [562] _Vide_ _F._ 407117, December, 1909. - - [563] _Met. Chem. Eng._ 1911, ~9~, 543. - - -~Other Alloys.~--On account of the great affinity of the cerium metals -for oxygen, misch-metal has been suggested as a reducing agent,[564] as -have also the alloys of cerium and magnesium;[565] the formation of the -latter is endothermic, so that they act much more vigorously than either -metal separately. The alloys of cerium with tin and aluminium have been -thoroughly investigated from the stand-point of metallography, by -Vogel.[566] It has recently been claimed that the addition of very small -quantities of cerium to aluminium has a very marked effect, the rare -earth metal acting as a purifying agent,[567] and greatly improving the -properties of the aluminium. The cerium may be introduced as fluoride, -either to the electrolytic bath in which the aluminium is being -prepared, or to the latter metal, after preparation, in the fused state. -The most favourable effect is said to be produced by 0·2 per cent. of -cerium. - - [564] _Vide_, _e.g._ Escales, _D. R. P._ 145820, October, 1903. - - [565] Hirsch, _loc. cit._ - - [566] _Zeitsch. anorg. Chem._ 1911, ~72~, 319; 1912, ~75~, 41. - - [567] Borchers and Barth, _D. R. P._ 246484, May, 1912. - - -~Applications of the Cerium Compounds.~[568]--One of the earliest -investigations in which cerium compounds were examined with a view to -technical employment, was that of Kruis,[569] who made experiments on -the comparative value of the salts of different metals as catalysts in -the manufacture of aniline black. He showed that a solution of aniline -with an oxidising agent (potassium chlorate or chromate) develops no -colouration unless a salt of a heavy metal is present. In the case of -the fabric impregnated with the solution, the only metals of which -compounds were found suitable for producing a colour were copper, which -was then generally used for the purpose, and cerium, iron, and -manganese. Of these, cerium, used in the form of the double sulphate, -was found to be by far the most suitable, and moreover to have the -advantage that only small quantities are required; the price was at that -time too high to allow of its use, but it has since been employed.[570] -Cerium compounds have also been proposed as mordants for alizarin,[571] -but they do not appear ever to have come into general use. - - [568] An account of the various suggestions for the technical - employment of the rare earth elements, by Dr. Max Speter, will be - found in Dammer, _Die Chemische Technologie der Neuzeit_, Stuttgart, - 1910, vol. i. pp. 500-504. - - [569] _Dingl. Polyt. J._ 1874, ~212~, 347. - - [570] _Vide_ Buhrig, _Dingl. Polyt. J._ 1879, ~231~, 77; and _Abstr. - Chem. Soc._ 1879, ~36~, 683. - - [571] _Vide_ Witt, _Chem. Ind._ 1896, ~19~, 156. - -In photography, ceric sulphate has been employed for some time for the -purpose of ‘reducing,’ _i.e._ removing silver from over-developed -negatives.[572] It is said to act very evenly and rapidly, the small -quantity of free sulphuric acid required to hold the salt in solution -having no bad effect. More recently, cerium salts have been proposed for -use in colour photography.[573] An emulsion is obtained by adding salts -of iron, uranium, or cerium to a colloidal solution of albumen in -ammonia, borax solution, or sodium carbonate solution; this is spread on -the paper or negative, and is said to be readily sensitive to light. - - [572] _Vide_ Lumière, _Bull. Soc. franc. Photog._ (2) 1900, ~16~, 103. - Also _E._ 470, 1900. - - [573] Fateau, _E._ 20740, 1907. - -The crude mixture of cerous sulphate with basic sulphates of other -elements of the cerium group, which has been patented for use as a -catalyst in the contact process for the manufacture of sulphuric -acid,[574] is prepared from the earth compounds obtained as by-products -in the treatment of monazite. These are converted into the sulphates, -and, after evaporation of the excess of sulphuric acid, heated for -several hours at a low red heat (300°-600°C.). The porous mass is then -broken, and is ready for use. It is stated that a nearly quantitative -yield of sulphur trioxide is obtained, and that the mixture acts more -efficiently than pure cerous sulphate. The reaction is said to depend on -the continuous formation and decomposition of the ceric salt, thus: - - Ce₂(SO₄)₃ + SO₂ + O₂ = 2Ce(SO₄)₂ - 2Ce(SO₄)₂ = Ce₂(SO₄)₃ + SO₃ + O - - [574] Hölbling, _D. R. P._ 142144 and _F._ 326321 of May, 1903. - -This process does not appear to have come into general use. - -A general patent had been taken out in 1901, protecting the use of -oxides of the rare earth elements for ‘high-temperature catalysis’ in -the manufacture of sulphuric acid,[575] but the oxides do not seem to be -very efficient.[576] - - [575] Meister, Lucius and Brüning, _E._ 1385, 1901. - - [576] _Vide_ Plüddemann, Dissertation, _Beitrag zur Aufklärung des - Schwefelsäurekontaktprozesses_, Berlin, 1907. - -It has also been proposed to utilise the oxidising power of ceric salts -in acid solution[577] for the preparation of aldehydes, quinones, etc., -from aromatic hydrocarbons, for which purpose they are claimed to be -more efficient than chromates. By the use of a crude cerium dioxide -(60-70 per cent. CeO₂) obtained by the ignition of the by-products of -the thorium industry, good yields were obtained of benzaldehyde, -naphthaquinone and anthraquinone from toluene, naphthalene and -anthracene respectively. - - [577] Meister, Lucius and Brüning, _D. R. P._ 158609, March, 1905. - -Garelli[578] has examined the action of cerium salts in tanning; he -states that with neutral solutions, effects very similar to those -produced by aluminium salts are obtained, but Eitner, who has also -examined the question,[579] is of opinion that the cost of isolating and -purifying the salts from the monazite residues renders their employment -for this purpose impossible. - - [578] _J. Soc. Chem. Ind._ 1912, ~31~, 830. - - [579] _Ibid._ 1911, ~30~, 1128. - -The fluoride, silicofluoride, and dioxide have also been proposed for -the preparation of enamels,[580] but do not give satisfactory results. - - [580] Rickmann and Rappe, _D. R. P._ 99165, September, 1898; also _D. - R. P._ 203773, October, 1908. - -Several patents protect the use of rare earth compounds for flashlight -powders. For most of the mixtures covered, it is claimed that the usual -defects of fumes, slow firing, etc., are absent. The usual recipes[581] -are for magnesium or aluminium powder with chromates, nitrates, or -similar salts of thorium, cerium, etc.; in one case[582] the rare earth -metals, alloyed with barium, silicon, uranium, or titanium, are to be -used with ‘an oxidising agent which leaves a non-volatile residue.’ None -of these mixtures appears to have been successful. - - [581] _Vide_, _e.g._ _E._ 14692, 1908; _D. R. P._ 158215. - - [582] _F._ 403722, October, 1909. - -Cerium compounds have also been proposed for use in arc-lamp electrodes; -it is claimed that they give a very intense light, one patent[583] -adding that the presence of cerium peroxide and a little fluorspar -causes the arc to burn evenly and quietly. In another, the use of a -mixture of tungstates or molybdates of the alkaline earths, with -fluorides of the rare earth elements is protected;[584] the use of -pyrophoric alloys, either entirely, or for the core of the electrode, -has also been suggested.[585] - - [583] _E._ 414707, June, 1910. - - [584] _F._ 431040, August, 1911; also _E._ 21374, 1909. - - [585] _E._ 8150, 1909. - - -~The Nernst Lamp.~--The first efforts which were made for the employment -of electricity in illumination endeavoured to utilize the heat produced, -when a current traverses a very thin metallic filament, to raise the -conductor to incandescence. Numerous efforts were made to adapt platinum -to this purpose, but its melting-point was finally admitted to be too -low; at length it was found possible to produce carbon filaments, and -the well-known carbon lamps came into use. Numerous attempts were made -to effect improvements;[586] one plan was to coat the carbon filament, -after its production, with a skin of metallic conductor, and zirconium -and thorium were among the metals proposed in this connection.[587] The -first really important advance, however, was effected by Nernst, who -took up the study of ‘conductors of the second order,’ and within a few -months succeeded in adapting these to the purposes of illumination -(1897-1898). The Nernst lamps gave a very intense white light with -considerably less consumption of electricity than the carbon filament -lamps; they enjoyed a very considerable vogue for some years, but have -been almost entirely displaced by the cheaper metal filament lamps, -which were occupying the attention of Auer von Welsbach at the time -Nernst perfected his invention.[588] - - [586] The reader is recommended to consult the _Jahresberichte über - die Leistungen der Chemischen Technologie_ of Fischer, Section - ‘Beleuchtung,’ for the years 1898-1901 inclusive, from which some idea - may be obtained of the innumerable proposals and suggestions, usually - protected by patent, which were put forward at this time. - - [587] _Vide_, _e.g._ _D. R. P._ 153959. - - [588] _Vide_ _E._ 1535, 13116 and 17580, 1898. - -In his first patent,[589] Nernst proposed the use of a rod of magnesia -or zirconia as filament; these oxides, which belong to his class of -conductors of the second order, are non-conductors at ordinary -temperatures, but their resistance decreases as the temperature rises, -so that at high temperatures they will conduct electricity at the -ordinary voltage. The preliminary heating was at first effected by means -of a Bunsen burner, but a later patent[590] of the same year protects a -method of heating by means of a platinum spiral in an auxiliary circuit, -which is automatically cut out when the current in the main circuit, -bearing the filament, attains its required strength. In the following -year[591] it was found that filaments composed of mixtures of oxides -were far more suitable than the earlier magnesia or zirconia rods; -yttria, thoria, and zirconia were the chief oxides used, small -quantities of ceria being occasionally introduced. With these filaments, -the increase of conductivity with temperature is far more rapid than -with the pure oxides; the preliminary heating required, therefore, is -less and the light obtained more intense. The filaments used were in the -form of rods or spirals obtained by compressing the powdered oxides. - - [589] _E._ 19424, 1897. - - [590] _E._ 23470, 1897. - - [591] _E._ 6135, 1898. - -The Nernst filaments differ markedly from those of the ordinary electric -glow lamp in that they are not conductors in the ordinary sense (or of -the first order, as Nernst puts it) but electrolytes, the passage of the -current being actually attended by an electro-chemical change in the -filament.[592] The oxide is ionised; the ions of the metals travel to -the cathode or negative pole, where the liberated atoms of metal -instantly recombine with the oxygen of the air, whilst oxygen ions -travel to the anode, from which the gas is liberated. There is thus a -gradual redistribution, resulting in accumulation of oxide at the -cathode with a corresponding loss at the anode, which is balanced, after -some time, by diffusion, so that equilibrium is attained. In consequence -of this redistribution the filament glows more brightly at the anode, -where it is thinnest, than at the cathode. - - [592] _Vide_ Nernst, _Zeitsch. Elektrochem._ 1899, ~6~, 41. - - -INDUSTRIAL APPLICATIONS OF ZIRCONIUM - -It has already been mentioned that zirconium received considerable -attention as a suitable substance for the preparation of metallic -filaments during the early stages of their development. Whilst at the -present time this element has been abandoned for the purpose,[593] -several zirconium lamps were at one time on the market, and a brief -mention of some of the work done in this direction may not be out of -place. - - [593] _Vide_ Baumhauer, _Zeitsch. angew. Chem._ 1910, ~23~, 2065. - -One of the general methods for the preparation of the metallic filaments -may be illustrated by a patent taken out in 1902 by Sander,[594] for the -preparation of filaments of zirconium, with or without addition of -zirconium carbide. The metal, or a compound which on heating will yield -the metal and a volatile substance which can be removed, is prepared in -a finely divided condition, and made into a paste with some organic -binding material; the paste is then forced through a tiny aperture, and -the resulting thread is shaped and heated to a high temperature _in -vacuo_ or in an inert atmosphere. If an organic substance be used to -form a paste with metallic zirconium, the final process of heating -results in the formation of the carbide; the same compound is also -obtained by another process protected by Sander (_loc. cit._) in which -the hydride of zirconium, prepared by the reduction of the oxide by -means of powdered magnesium in an atmosphere of hydrogen, is mixed with -a cellulose solution, and the liquid treated as in the manufacture of -artificial silk, the threads obtained being then heated to remove all -organic matter as far as possible. - - [594] _D. R. P._ 133701, July, 1902. - -The carbide is also probably obtained by the process of the British -Thomson-Houston Company, in which advantage is taken of the fact that -zirconium oxalate is a pasty gelatinous substance, which can be forced -through a die to form a thread without addition of any agglutinating -agent. The oxalate, precipitated by addition of ammonium oxalate to a -solution of a zirconium salt, is mixed with finely divided carbon, and -the threads obtained from the pasty mass heated to a very high -temperature in a furnace.[595] Zirconium oxalate is also proposed as a -binding material for powdered tungsten, in the preparation of filaments -from that metal.[596] - - [595] _E._ 5415, 1908. - - [596] _E._ 10590, 1908. - -The compounds of zirconium and thorium with elements of group VB, -according to two German patents,[597] are suitable for the preparation -of metallic filaments in much the same way. Thorium, titanium, and -zirconium are also among the metals which, it is claimed, can be -obtained in the pure fused state by heating in an electric arc _in -vacuo_, so that filaments can be drawn directly.[598] - - [597] _D. R. P._ 153958 and 154299, September, 1904. - - [598] _Ibid._ 169928, April, 1906. - -Metallic zirconium and its alloys have recently been employed in -metallurgy. The pure metal can be obtained by the calcium reduction of -Kuzel and Wedekind (_vide_ p. 316); zirconia is not reduced by powdered -aluminium (Goldschmidt’s process), but alloys of zirconium and iron can -be easily obtained by the reduction of mixtures of the two oxides by -this method. Alloys can be obtained containing up to 35 per cent. of -zirconium; this ferro-zircon, as it is called, has been used to some -extent recently in place of ferro-titanium (_vide infra_) for the -purification of steels.[599] Addition of small quantities of zirconium -to steels, brass, copper, etc., is said to secure sound castings, and to -increase considerably the strength and resistance to acids of the metal. - - [599] _Vide_ Weiss, _E._ 29376, 1910, and Lesmüller, _D. R. P._ - 231002, February, 1911. - - -~The Technical Uses of Zirconia.~--Since the discovery of Baddeleyite, -the natural oxide of zirconium (_vide_ p. 75), which occurs in large -quantities in Brazil, many proposals have been brought forward for the -employment of this compound. Its application to the manufacture of -glasses and enamels will be referred to in the next chapter. Patents -have been taken out protecting its use for the preparation of white -pigments,[600] as a toilet-powder,[601] and as a polishing powder,[602] -for it is extremely stable towards chemical reagents, very voluminous, -and at the same time very hard. It has long been employed for coating -the lime and magnesia pencils used in the Drummond or ‘lime’ light; and -recently it has been employed for the headlights of automobiles, in the -Blériot lamp,[603] in which a rod of zirconia is heated in a blowpipe -flame fed with oil vapour and oxygen. - - [600] _D. R. P._ 235495. - - [601] _Ibid._ 237624. - - [602] _Ibid._ 230757. - - [603] _Ibid._ 174313, September, 1906. - -By far the most important property of the oxide, from the technical -point of view, is the ease with which it resists high temperatures. The -natural oxide can be freed, to a very large extent, from the iron oxide -which it encloses, by the prolonged action of hydrochloric acid; -experiments were carried out on the material so obtained by -Simonis,[604] who showed that by prolonged heating at a high -temperature, the remaining impurities, chiefly ferric oxide and silica, -could be volatilised, leaving the zirconia unchanged. Riecke[605] showed -that whilst the oxide is very suitable for the manufacture of highly -resistant crucibles, its use is restricted by the fact that it is easily -reduced by carbon at high temperatures, forming the carbide. - - [604] _Sprechsaal_, 1908, ~41~ (1), 210. - - [605] _Ibid._ 214. - -Weiss and Lehmann have carried out exhaustive experiments on the -preparation of crucibles of zirconia.[606] They worked first with -mixtures of zirconia and magnesia, with phosphoric acid as a binding -material; the best results were obtained with a mixture of 90 per cent. -zirconia and 10 per cent. magnesia, which gave extraordinarily resistant -crucibles. Prolonged heating at temperatures over 1900°C. eliminated -all the phosphoric acid by volatilisation; the crucibles could then be -heated in the blowpipe flame and plunged immediately into cold water -without cracking or breaking, and were not affected by fused sodium -hydroxide or potassium hydrogen sulphate. Crucibles were also made with -the addition of potassium and sodium salts, and were found to answer -very well; platinum could be melted in them to a mobile liquid. Similar -crucibles are already on the market. - - [606] _Zeitsch. anorg. Chem._ 1910, ~65~, 218. - -As early as 1904 the use of zirconia was suggested for coating -muffles, retorts, and tubes which are required to withstand high -temperatures.[607] In 1906 it was proposed[608] for the manufacture of -crucibles in which rock-crystal (quartz) is fused for the preparation of -quartz-glass, since zirconia is not attacked by molten silica. It -promises to be of the greatest use in all cases where a very refractory -material, stable towards the ordinary chemical reagents, is required. - - [607] Pufahl, _D. R. P._ 156756. - - [608] Heræus Co., _D. R. P._ 179570. - - -CHAPTER XXII - -THE INDUSTRIAL APPLICATIONS OF TITANIUM AND ITS COMPOUNDS - -Though probably at least as plentiful in nature as most of the common -metals, titanium has always, until quite recently, been regarded as one -of the rare elements. Of its chemistry, very little indeed was known, -and it is improbable, even now, that the pure element has been isolated. -It had no technical value; indeed, its commonest ore, ilmenite or -titaniferous iron ore, was sedulously avoided by manufacturers, who -considered that even very small percentages of the element rendered an -iron ore valueless because unsuitable for working in blast furnaces. -Towards the end of the last century, one or two metallurgists had -demonstrated that ilmenite, under the proper working conditions, would -yield a pig iron of very good quality when smelted in the blast furnace, -but it was left for the long and arduous researches of Kossi to show -that the element is possessed of properties which render it very -valuable for metallurgical purposes. Since the successful culmination of -his work in the first few years of the present century, titanium has -attained considerable importance in the treatment of special steels for -rails, car wheels, crushing machinery, etc. At present, titaniferous -iron ores are being worked on a large scale, and many titanium compounds -are coming into use for technical purposes. - -The titanium minerals of commercial importance are rutile and ilmenite -(_vide_ Part I. pp. 57 and 77). The former, the pure titanium dioxide, -is of fairly wide distribution, but ilmenite occurs in far greater -quantities, forming deposits of enormous dimensions, especially in -America, as, _e.g._ in New York Co. and Quebec. Owing to its high -melting-point and relatively low specific gravity, metallic titanium -can only be incorporated with molten steels with the greatest -difficulty, and for this reason alloys of titanium and iron, known -technically as ferro-titanium, are usually employed for the treatment of -steels. For the preparation of ferro-titanium, ilmenite of good quality -is as suitable as rutile, and, of course, far cheaper; hence the latter -is only employed for the preparation of titanium salts for use in -colouring and mordanting, and for titanium compounds for arc-lamp -electrodes, etc. - -Various processes are employed for the manufacture of ferro-titanium -from ilmenite. In cases in which a considerable percentage of carbon is -not undesirable, for instance, where the alloy is required for the -treatment of cast iron or of high-carbon steel, the mineral is reduced -directly with carbon in an electric furnace; the ferro-titanium so -obtained usually contains from six to eight per cent. of carbon. For -pure iron-titanium alloys, the process worked out by Rossi[609] is used -in America almost entirely. Ilmenite is charged into a bath of molten -aluminium, heated electrically; the mineral is at once attacked, with -formation of iron, in which the titanium dissolves as reduction -proceeds. This process may also be used for reduction of rutile, if -scrap iron is added to the aluminium bath, to allow of the formation of -the required alloy. In Germany, the Goldschmidt or ‘thermite’ reaction -is largely employed; powdered ilmenite is intimately mixed with the -calculated quantity of aluminium powder, reduction being started as -usual by means of a fuse of magnesium ribbon imbedded in a small -quantity of barium peroxide. - - [609] _Elect. chem. Ind._ 1903, ~1~, 523. - -Quite recently, the question of the separation of titanium compounds -from ilmenite used for the manufacture of pig iron has attracted -considerable attention. It has been already mentioned (_vide supra_) -that titaniferous iron ores have been shown to be perfectly amenable to -blast-furnace treatment, the old and deeply rooted idea that -titanium-bearing slags are stiff and troublesome being entirely contrary -to facts, when suitable conditions are observed;[610] moreover, it is -shown that the pig iron obtained is of unusually good quality. Rossi -has suggested[611] that if sufficient carbon be added to reduce all the -silica and oxides of iron, with enough lime to slag off the titanium -dioxide as calcium titanate, the latter can be used as a source of -titanium compounds or alloys, whilst a ferro-silicon will be obtained as -pig metal; the temperature must be carefully adjusted to ensure -reduction of the silica without loss of titanium dioxide. Another -patent[612] proposes the reduction of the ore in an electric furnace, -and the treatment of the crude ferro-titanium in a converter with a -blast of air or nitrogen; the titanium nitride formed is then driven out -of the metal by a blast of superheated steam--any ammonia or cyanogen -formed being collected--and removed, the iron remaining being -‘Bessemerised’ directly in the same converter; the titanium nitride can -be used as a manure, or for the manufacture of ammonia or nitric acid -(_vide infra_). The removal of iron as the volatile carbonyl has also -been suggested,[613] the titanium being subsequently transformed into -the nitride. - - [610] _Vide_, _e.g._ _Iron Age_, 1909, ~84~, 1149 and 1223. - - [611] _E._ 3582, 1901. - - [612] Sinding-Larsen and Willumsen, _D. R. P._ 220544, April, 1910. - - [613] Sinding-Larsen, _E._ 17632, 1910. - - -~Employment of the Element in Metallurgy.~--It has been already -mentioned that titanium itself is quite unsuitable for direct -incorporation with steel. Besides the relatively low specific gravity -(5·2), which would render mixing very difficult, the very high -melting-point (given by Weiss and Kayser[614] as 2350°) would prevent -uniform dissemination. The element is therefore generally used in the -form of a ferro-titanium of low titanium content, 10-15 per cent. being -the proportion usually employed. The addition should be made at the end -of the Bessemer process, and after the addition of the required -quantities of manganese and silicon alloys; the calculated quantity of -ferro-titanium is added as the steel runs from the converter into the -ladle. A suitable proportion is said to be one-half per cent. of alloy, -so that the actual proportion of titanium to steel is somewhere about -1·5-1·8 lb. per ton. Six or eight minutes should be allowed after the -addition, for the titaniferous slag to come to the surface. - - [614] _Zeitsch. anorg. Chem._ 1910, ~65~, 345. - -Although low percentage ferro-titanium is usually employed, it has been -stated that high-percentage alloys, and even the element itself, are -immediately taken up by steel if aluminium be added at the same time. -Thus Venator[615] states that if titanium and aluminium be added -together to the bath, both elements are immediately taken up, the -reaction being very rapid and complete; the effects produced by the -titanium are in no way influenced by the presence of the aluminium. -Goldschmidt[616] proposes the use of ferro-titanium containing 24-25 per -cent. of the element, with 3 per cent. of aluminium; this dissolves very -readily, is very effective, and moreover, can be very easily prepared by -the alumino-thermic reaction. - - [615] _Stahl Eisen_, 1910, ~30~, 650. - - [616] _D. R. P._ 235461, June, 1911. - -In some cases, where it is desired to treat a steel both with silicon -and with titanium, ferro-alloys containing both of these elements may be -employed. By reduction of ilmenite or rutile with carbon in an electric -furnace, in presence of silica, Becket[617] obtains alloys of high -titanium and silicon content, which are said to dissolve very easily in -molten steels and to produce improved effects. The Titanium Alloy -Manufacturing Company have also patented[618] the preparation of -titanium-silicon alloys, with or without addition of iron or copper, by -the reduction of a mixture of rutile and quartz. - - [617] _U. S. P._ 940665 and 941553 of November, 1909. - - [618] _F._ 407858, January, 1910. - -Recently the use of ferro-titanium in the manufacture of pig iron has -attracted attention. For this purpose, alloys of very low -titanium-content (0·1-1·0 per cent.) are employed. Addition of very -small amounts of such alloys to the molten metal before casting is said -to have a marked cleansing effect,[619] resulting in much better and -stronger castings. - - [619] _Vide_ Slocum, _Chem. Eng._ 1911, ~13~, 257. - -Whilst it is very generally agreed that the addition of titanium results -in the production of much stronger and more durable products, the -question of the precise effect obtained is by no means definitely -settled. The experimental work, whilst pointing on the whole to the -superiority of titanium-treated steel, is by no means conclusive; in -some cases, indeed, it is conflicting. Thus the micro-photographs -obtained by von Maltitz[620] and Venator[621] show that the -titanium-treated steel has a far cleaner fracture and far more -homogeneous structure than steels not so treated; on the other hand, the -micro-photographs of Treuheit[622] show practically no improvement in -structure for the titanium steel. The exhaustive tests of the first two -authors, again, and the experiments of numerous railways in the use of -titanium steel rails,[623] demonstrate clearly that the treatment -results in improvement in strength and durability of the product; but -the work of Otto[624] proves equally clearly that his products did not -differ markedly, whether titanium-treated or not, and he is of opinion -that the rail tests were not sufficiently prolonged or searching to be -considered conclusive. It is nevertheless to be considered certain that -the use of titanium does cause a marked improvement in the quality of -the steels obtained, and especially in the durability of rails. The -negative results obtained by some authors may be explained, firstly, on -the ground that no tests are conclusive unless carried out with steel -from the one bath, one half of which has been treated with titanium, and -the other half not so treated; secondly, that the ferro-titanium must be -incorporated with the metal, and must not be suffered to be taken up by -the slag, and so lost; and thirdly, that the bath must be allowed to -remain for some minutes after treatment, in order that the reaction may -be complete, and the titanium-bearing slag allowed to rise to the -surface. When these conditions are carefully observed, experiment shows -that marked improvement in the quality of the steels produced is -effected. - - [620] _Stahl Eisen_, 1910, ~29~, 1593. - - [621] _Ibid._ 1910, ~30~, 650. - - [622] _Ibid._ 1910, ~30~, 1192. - - [623] _Vide_ Dudley, _J. Ind. Eng. Chem._ 1910, ~2~, 299; also _Cass. - Mag._ 1911, ~40~, 483. - - [624] _Vide_ abstract in _Stahl Eisen_, 1912, ~32~, 1497. - -As to the actual nature of the effect produced, it is generally believed -that titanium acts merely as a cleansing agent, freeing the metal from -occluded or combined gases, and removing blow-holes, so producing a -denser and more homogeneous structure, with consequent improvement in -properties. The added titanium is usually found entirely in the slag, -so that it appears certain that it does not alloy, but merely purifies. -It certainly acts as a powerful and rapid deoxidiser, removing the last -traces of the gas which have escaped the action of the manganese, -silicon, etc., with which steels are now generally treated. Many -authorities, on the ground of analyses, and of the known affinity of -titanium for nitrogen, believe that it very largely reduces the -nitrogen-content,[625] which is so harmful; this, however, is still an -open question.[626] It is stated that if excess of titanium is used, so -that small quantities--0·05-0·20 per cent.--remain in the finished -steel, the toughness and durability are further increased;[627] but as a -rule, manufacturers prefer to work with smaller quantities, so that no -free titanium remains in the product. - - [625] _Vide_ von Maltitz, _loc. cit._ - - [626] _Vide_ Venator, _loc. cit._ - - [627] _Vide_ _Bull. Imp. Inst._ 1911, ~9~, 134. - - * * * * * - -The preparation of alloys of titanium with almost all the commoner -metals is protected by patent, but few of these are of technical -importance. Small quantities of titanium are said to improve very -considerably the properties of copper and its alloys, the brasses, -bronzes, etc., especially in castings. The addition is usually made in -the form of an appropriate titanium alloy, prepared by reduction of the -mixed oxides with carbon in an electric furnace, or treatment of the -mixed oxides, together with the alloying metal, with aluminium under -similar conditions.[628] The titanium-silver alloys obtained in this -way[629] are said to improve greatly the structure of silver, by -preventing the familiar ‘spitting’ as the fused metal cools. - - [628] _Vide_ Rossi, _U. S. P._ 986505, March, 1911; 935863, October, - 1909, etc. - - [629] Rossi, _U. S. P._ 1024476 and 1025426, August, 1912. - -An interesting process, which has been patented by Rossi,[630] recalls -the method of formation of cementation steels. He has found that if a -metal be loosely covered with its alloy with titanium, in a finely -powdered condition, and the whole heated, the titanium diffuses into the -metal, to a depth and concentration which vary with the temperature and -the time of heating. He suggests that in this way a metallic body may be -toughened and strengthened at any desired point, _e.g._ steel for -armour-plate at the surface. Whether the process will be of any -technical value or not can only be shown by experiment. - - [630] _U. S. P._ 986504, March, 1911. - - -~Application to Arc-lamp Electrodes.~--During the last fifteen years, -innumerable efforts have been made to adapt titanium and its compounds -to the manufacture of arc-lamp electrodes, or pencils.[631] The -spark-spectrum of titanium is very rich in lines, and in respect of -light efficiency, the element is very suitable for the purpose; the -experimental difficulties, however, have been very great, and though -electrodes containing titanium compounds have been on the market for -some years, the problem cannot be said to have been satisfactorily -solved. The best pencils contain titanium carbide, but successful -attempts have been made to use the oxide. As early as 1904, Weedon[632] -proposed an electrode prepared by heating 7 parts (1 mol.) of the -dioxide with 1 part of carbon to 1500°-2000°C.; the ‘sub-oxide’ produced -was powdered, worked up into a paste with a suitable binding material, -and forced through a nozzle. The sticks so obtained, after drying and -baking in the usual manner, were said to give satisfactory results, but -consumption is very rapid, and troublesome deposits of the dioxide are -formed at the end of the electrode. The dioxide, which alone is a very -bad conductor, enters directly into the composition of the so-called -‘magnetite’ pencils, which are best made[633] by fusing together -magnetite, rutile, and chromite, in suitable proportions, with a little -potassium fluoride, powdering the brittle mass, and using this to form a -paste from which the pencils may be obtained as usual. These electrodes -are said to give a very efficient and fairly steady arc. They have the -disadvantage that tiny glowing particles are thrown off, which soon -render the globes opaque; the addition of sulphur[634] to the powder -during manufacture is said greatly to diminish this inconvenience. -Pencils made in a similar manner from powdered ferro-titanium[635] do -not appear to have come into use. - - [631] _Vide_, _e.g._ Ladoff, _J. Ind. Eng. Chem._ 1909, ~1~, 711. - - [632] _E._ 26921, 1904. - - [633] _E._ 2027, 1909. - - [634] _E._ 18965, 1909. - - [635] _U. S. P._ 840634, January, 1907. - -The carbide alone is a good conductor, and gives a very satisfactory -light,[636] but electrodes made from this compound without additions -have several disadvantages. The life is short, and the arc soon becomes -flickering and unsteady. A deposit of the badly conducting dioxide -gradually accumulates on the anode, and once the current has been -interrupted, this deposit renders it very difficult to strike the arc -again. These disadvantages are largely overcome by a series of -improvements recently patented in Germany by the Allgemeine -Elektrizitäts Gesellschaft of Berlin. Addition of small quantities--4·5 -per cent.--of chromium carbide increases the length of life;[637] the -unsteadiness and flickering are greatly diminished by incorporation of -powdered coke, cryolite and fluorspar,[638] or better, of the -titanofluoride of calcium or cerium,[639] whilst the addition of finely -divided sulphur (or selenium or tellurium)[640] greatly reduces the -disadvantage due to the throwing off of incandescent particles. The -British Thomson-Houston Company patents a similar electrode,[641] in -which a carbon-mixture is used instead of coke, and the electrode is -manufactured with a carbon shell. For this purpose, the paste prepared -from the powdered mixture may be filled into a hollow carbon rod, or the -lightly baked pencil may be coated with pitch and heated to a high -temperature. The use of a mixture of cerium fluoride and tungstate, with -carbon and cryolite, is also said to prevent flickering.[642] - - [636] Weedon, _Trans. Amer. El. chem. Soc._ 1911, ~16~, 217. - - [637] _D. R. P._ 231231, February, 1911. - - [638] _Ibid._ 233125, March, 1911. - - [639] _Ibid._ 251837, October, 1912. - - [640] _Ibid._ 234466, May, 1911. - - [641] _E._ 6500, 1912. - - [642] Guay, _U. S. P._ 1039522, September, 1912. - -In arc lamps in which pencils containing titanium compounds are used, -the anode is generally made of copper, and is placed below the cathode, -the reverse being the case where carbon electrodes are employed. The -copper is inactive, and contributes nothing to the light; if the anode -be of suitable dimensions, it wears away very slowly, whereas the -cathode, containing the titanium compound, is rapidly consumed. In lamps -in which carbon electrodes are used, the light is emitted chiefly from -the extremities of the electrodes, the path of the arc being -comparatively non-luminous; the light has the familiar reddish-yellow -colour characteristic of the earlier forms of arc lamps. Where titanium -pencils are employed, however, the light is emitted almost entirely from -the arc itself, the electrodes contributing very little, and is of a -pure white colour, very different from that of the carbon lamp. - -Attempts have been made to employ titanium in the manufacture of metal -filaments for glow lamps. The metal would be very suitable for this -purpose, by reason of its high melting-point and low conductivity, but -the difficulty of obtaining it in the pure state, and the remarkable -susceptibility of the filament to traces of impurity, have so far proved -insuperable. For the sake of illustration, a proposal put forward in -1908 may be briefly referred to.[643] Pure titanium dioxide is heated in -a stream of ammonia; the nitride obtained is decomposed at 1200° _in -vacuo_, and after cooling, the metal is powdered and made into a paste -with a solution of albumen in ammonia. The threads obtained from this in -the usual manner are heated to 1200° in an electric furnace; the carbon -deposited from the albumen forms the cyanide by reaction with the trace -of nitride which has escaped decomposition, or which has been formed by -further action of ammonia. The cyanide is volatile, and can be removed -at high temperatures _in vacuo_, leaving a sintered filament of the -metal. So susceptible is the filament to impurity, that the trace of -carbon deposited from the vapour of the oil of the pump which diffuses -into the vacuum is sufficient to render it so fragile as to be -useless.[644] - - [643] Trenzen and Pope, _E._ 14852, 1908. - - [644] _Vide_ _Bull. Imp. Inst._ 1911, ~9~, 134. - - -~Titanium Compounds in Dyeing and Colouring.~--The use of titanium -compounds as mordants in the dyeing of leather and textile goods has -been known for a considerable time.[645] As early as 1896, a patent was -taken out by Barnes[646] for the treatment of prepared animal skins by -immersion in a bath of a titanium salt. Subsequent boiling or steaming -causes hydrolysis, with precipitation in the skin of hydrated titanium -dioxide, which forms lasting dye-lakes when the fabric is immersed in -the dye-bath. Whilst this treatment has been found satisfactory with -some classes of leather goods,[647] more delicate kinds are liable to be -injured by the mineral acid set free, and numerous patents protecting -the preparation and employment of organic salts of the element have been -taken out by Dreher.[648] The same investigator[649] has discovered that -excellent results can be obtained in the cold by the addition of various -‘Hülfsalze,’ which are chiefly acetates or formates of the alkaline -earth metals, chromium, or aluminium, or basic salts of the last two. -Double decomposition of these with the titanium salt forms basic or -highly hydrolysed salts of the latter, so that the hydrated oxide or a -basic compound is formed on the fabric. - - [645] A good account of some of the earlier work in this connection is - given by Erban, _Chem. Zeitg._ 1906, ~30~, 145. - - [646] _E._ 5712, 1896. - - [647] _Vide_ Dreher, _D. R. P._ 142464, June, 1903. - - [648] _Vide_ _E._ 22629 and 23188 of 1901, 14921 and 27597 of 1902, - and 5211 of 1903. - - [649] _Vide_ _D. R. P._ 139059 and 139060 of February, 1903, and - 139838 of March, 1903. - -The titanium salts specified in these patents are salts of the element -in the tetravalent condition, prepared from rutile by the action of -strong mineral acids. As early as 1902, the technical preparation of -salts of trivalent titanium for reducing purposes was patented by Spence -and Spence, of Manchester.[650] The process is an electrolytic one, and -is effected in a cell divided into two compartments by a porous -partition, one electrode being introduced into each compartment; an -electromotive force of 3-4 volts is required. A 20-25 per cent. titanium -tetrachloride solution is introduced into the cathode compartment, and -dilute hydrochloric acid into the anode compartment; on electrolysing, -chlorine is evolved at the anode, and may be utilised as usual in the -preparation of bleaching powder, etc., whilst the tetrachloride in the -cathode compartment is reduced to trichloride. The solution is then -concentrated at 65°-70°C. under reduced pressure, and the crystalline -trichloride separated. In the preparation of the corresponding sulphate, -sodium sulphate must be present in the cathode compartment, and a double -salt is obtained; the process is carried out in lead-lined cells, in -presence of excess of sulphuric acid. The preparation of the -sesquioxide, Ti₂O₃, free from compounds of aluminium and iron, was also -suggested by Dreher[651] by reduction of the acid solution of the impure -or mixed salts with zinc or sodium amalgam, and approximate -neutralisation; the sesquioxide differs from the dioxide in that it -separates while the solution is still somewhat acid, which the hydrated -oxides of iron and aluminium will not do. Dreher suggested that the -strong reducing properties of the sesquioxide and its salts should make -these valuable for bleaching, colour-printing, and similar purposes. - - [650] _E._ 16238 and 18108 of 1902. - - [651] _E._ 1835, 1903. - -More recently[652] the reduction of titanium salts by means of aluminium -powder has been suggested; in the case of the sulphate, the aluminium -salt formed may be partly eliminated as alum, in the ordinary way, if -desired, but it is claimed that its effect is beneficial rather than -harmful. The preparation of organic double basic salts of trivalent -titanium,[653] which hydrolyse very readily, suggested the use of such -compounds as mordants and for reducing purposes. These salts may be -prepared fairly easily[654] by adding concentrated solutions of the -appropriate potassium, sodium, or ammonium salts in excess to -concentrated solutions of the trichloride, in absence of air. The double -salts separate, and are washed and dried; in this condition they are -fairly stable, but the solutions hydrolyse at once on merely warming, -with separation of the hydrated sesquioxide. On this account, and also -because of the strong reducing action, these compounds are likely to -prove valuable as mordants, and for other purposes. - - [652] Spence, Craig, and Spence, _E._ 13260, 1911. - - [653] Stähler and Bachran, _Ber._ 1911, ~44~, 2912. - - [654] Kunheim and Co. and Stähler, _D. R. P._ 284251, June, 1912. - -Titanium compounds have frequently been suggested for the preparation of -colouring-matters; the ferrocyanide has a fine green colour, and is used -to some extent in place of arsenical pigments for the preparation of -coloured wall-papers, whilst the dioxide is of some value for tinting -artificial teeth, porcelain tiles, etc. Yellow and reddish-yellow -pigments are produced from rutile and ilmenite by various methods. A -fine covering paint is said to be obtained by a process[655] in which -ilmenite is powdered and roasted to 500°C.; the cooled product is -crushed with water, and after one or two washings to remove soluble -compounds, yields a very finely divided orange-yellow suspension, the -precise shade of which varies with the duration and temperature of the -roasting. The product is at once thrown down from the suspension, by -addition of a small quantity of a salt solution, and so can easily be -obtained in the solid state. In another process,[656] the pulverised -ilmenite is warmed with concentrated sulphuric acid, in which it -dissolves with great development of heat; the excess of acid is removed -by evaporation and the mass calcined to decompose the sulphates. It is -stated that different shades may be obtained by carrying out the last -operation in an atmosphere of sulphur dioxide or other gas. - - [655] Farup, _E._ 3649, 1910; _F._ 412563, May, 1910. - - [656] _E._ 10368, 1911. - -In connection with the colouring properties of the oxides of titanium, -it is interesting to note that the blue colour of sapphires is probably -due to the presence of compounds of trivalent titanium; Verneuil[657] -has succeeded in preparing artificial sapphires in all respects -identical with the natural stones by fusing alumina with small -quantities of titanium dioxide and ferric oxide in the flame of the -oxyhydrogen blowpipe, which effects the reduction. - - [657] _Compt. rend._ 1910, ~150~, 185. - - -~Other Uses of Titanium Compounds.~--Owing to the high price of the tin -dioxide which is largely employed for the preparation of enamels and -opaque glasses, innumerable suggestions have been made for the -employment of the oxides of titanium and zirconium in this -direction.[658] A critical examination of the question has been made by -Grünwald;[659] he finds that the opacity consequent on addition of these -compounds increases with the amount of clay used, within limits, and -concludes that the effect is due to displacement of alumina by the -oxides, with formation of silicates of titanium and zirconium, which -dissolve in the melt. He states that the results obtained from the use -of these oxides are not comparable with those given when stannic oxide -is employed, and that therefore the former oxides are of little use for -this purpose. - - [658] _Vide_, _e.g._ _D. R. P._ 189364, 218316, 115016, 207001; _F._ - 438908, etc. - - [659] _Sprechsaal_, 1911, ~44~, 72. - -These two oxides find employment to a small extent in the manufacture of -‘Siloxide’ quartz glass.[660] Quantities up to 1·5 per cent., added to -the molten silica, reduce the difficulty of working the material. -Exhaustive tests carried out by Thomas[661] indicate that the vessels -made from this material are, on the whole, to be preferred to ordinary -quartz glass, resisting high temperature better, and showing less -tendency to become crystalline and therefore brittle when maintained for -considerable times at high temperature. - - [660] Wolf-Burckhardt and Borchers, _F._ 432786, October, 1911. - - [661] _Chem. Zeitg._ 1912, ~86~, 25. - - * * * * * - -Much work has been carried out during the last few years with the object -of utilising titanium compounds for the ‘fixation’ of nitrogen. - -The metal combines very vigorously with the gas at about 800°C. (_vide_ -p. 224), forming the nitride. If the gas, or air, be passed over a -heated mixture of the dioxide with powdered coke, formation of the -cyanonitride occurs at comparatively low temperatures (1100°-1300°C.) if -a small quantity of an alkali salt be present,[662] the action being -apparently catalytic; if excess of carbon is used, considerable -quantities of the cyanide may be formed. Numerous experiments carried -out by the chemists of the Badische Anilin- und Soda-Fabrik have shown -that at high temperatures, the action of water and a suitable oxidising -agent, or in the presence of metallic compounds, the action of steam -alone, will liberate considerable quantities of ammonia from both these -derivatives,[663] whilst in the presence of platinum compounds, if air -be pumped in, the higher oxides of nitrogen are formed. One or two -examples may be given: - - (1) Ti₂N₂ + 4NaOH + H₂O + 2CuO = 2NH₃ + Cu₂O + 2Na₂TiO₃--autoclave at - 180°C. - - (2) 2Ti₂N₂ + 2H₂SO₄ + 6H₂O + O₂ = 4TiO₂ + 2(NH₄)₂SO₄--autoclave at - 120°-140°C. - - (3) Ti₂N₂ + 3H₂O = Ti₂O₃ + 2NH₃--steam at 500°-600°C. - - [662] _Vide_ Bosch, _U. S. P._ 957842, May, 1910. - - [663] _Vide_, _e.g._ _D. R. P._ 202563 and 203748 of March, 1907; - 204204 and 204475 of November, 1908; _E._ 2414, 1908; _F._ 387002 of - June, 1908; _U. S. P._ 957843 of May, 1910, gives a résumé of all the - processes. - -In the second case, the oxygen is derived from air pumped into the -apparatus, and ferrous sulphate is used as a catalyst. In the third -case, a metallic salt, oxide, or hydroxide is required as a catalyst. - -In view of the success of the cyanamide method for the fixation of -atmospheric nitrogen, these processes, though of considerable -theoretical interest, do not seem likely to become of practical -importance. - - * * * * * - -One or two minor uses have been suggested for titanium dioxide. Small -quantities are fused with bauxite, silica, and ferric oxide in the -preparation of abrasives,[664] whilst a mixture with carbon is suggested -as a refractory body for linings, crucibles, etc., surface heating of -this forming a layer of highly resistant carbide.[665] An interesting -American patent protects the use of the dioxide for the preparation of -phosphorus pentoxide from bone-ash or natural calcium phosphate.[666] -The pulverised mixture of the phosphate and oxide is introduced at the -upper end of an inclined rotating furnace, by means of a hopper and -screw feed; fuel is fed in at the lower end, and an outlet is provided -for the periodic removal of the calcium titanate, etc., formed. The -silica and alumina of the impure phosphate, together with the titanium -dioxide introduced, displace the phosphorus pentoxide, which, being -volatile, escapes continuously through a special pipe; there is left a -mixture of silicate, aluminate and titanate of calcium, which may be -used as a source of titanium compounds. - - [664] Saunders, _U. S. P._ 954766, 954777, and 954778. - - [665] Becket, _U. S. P._ 1038827, September, 1912. - - [666] Peacock, _U. S. P._ 995897, June, 1911. - - -~Estimation of the Element.~--Owing to the difficulties of the -separation from the acidic oxides, silica, zirconia, and the pentoxides -of columbium and tantalum, and from the basic oxides, alumina and the -oxides of iron and tin, the estimation of titanium in a mineral or a -steel is usually a difficult and tedious process. Gravimetric as well as -volumetric methods are employed. In the former, the element is isolated -and weighed in the form of the dioxide; in the latter, standard -solutions of suitable oxidising agents are employed, advantage being -taken of the ease with which the element can be transformed from the -trivalent to the tetravalent condition. - -The mineral or steel in which the element is to be estimated is usually -fused with sodium hydrogen sulphate, which forms the sulphate. If -thorium, uranium or rare earths are present, treatment in the cold with -hydrofluoric acid is often more suitable; the acidic oxides are taken -into solution, leaving the more positive elements in the form of the -insoluble fluorides. Trautmann finds that steels or ferro-titaniums of -high silicon content are attacked only very slightly by fused sodium -bisulphate; he recommends[667] ignition to the oxides, evaporation with -hydrofluoric acid to remove silicon as the volatile tetrafluoride, and -fusion of the residue with bisulphate. - - [667] _Zeitsch. angew. Chem._ 1911, ~24~, 877. - -The bisulphate melt, after cooling, is leached with water, and the whole -boiled under a reflux condenser for several hours; this treatment should -throw down the oxides of titanium, columbium and tantalum, leaving -zirconium and aluminium in the form of the sulphates in the acid -solution; the addition of ammonia may be necessary to effect complete -hydrolysis. The acidic oxides may also be precipitated if the solution -be diluted and treated with excess of acetic acid before boiling. In -both cases, a considerable quantity of iron is thrown down. The -precipitated oxides are dissolved in the cold by dilute sulphuric acid -to which hydrogen peroxide has been added. - -For volumetric estimation, separation from iron is not generally -necessary. If gravimetric methods are to be employed, separation may be -effected in several ways. Titanium dioxide may be precipitated in a -fairly pure condition by reducing the solution with sulphur dioxide, and -boiling until the titanium sulphate has been completely hydrolysed. -According to Barneby and Isham,[668] this method gives low results; -these authors prefer to remove iron completely from the solution, and -then effect complete hydrolysis by addition of ammonium acetate and -acetic acid to the boiling solution. For this purpose, they dissolve -the mixed oxides in hydrochloric acid, and remove ferric chloride by -ether extraction. Bornemann and Schirmeister[669] precipitate titanium -dioxide completely by means of ammonia, holding iron in solution as -ferrocyanide; for this purpose, iron is completely reduced to the -ferrous state by means of sodium hydrogen sulphite, and solutions of -potassium cyanide and ammonia are added together to the warm liquid, -which is afterwards heated nearly to the boiling-point to effect the -precipitation. - - [668] _J. Amer. Chem. Soc._ 1910, ~32~, 957. - - [669] _Metallurgie_, 1910, ~7~, 723. - -Iron may also be removed by the ordinary methods, if some reagent be -previously added to hold titanium in solution. For this purpose, -tartaric acid and its salts are commonly used; none of the ordinary -precipitants will throw down the element if this reagent be present. -After addition of ammonium tartrate, iron is removed by means of -ammonium sulphide. After filtering, tartaric acid may be removed by -means of potassium permanganate, the manganese dioxide formed being -reduced with sulphur dioxide. According to Thornton,[670] evaporation -with a mixture of sulphuric and nitric acids is a more convenient method -of destroying the organic acid; titanium dioxide is then thrown down by -diluting and boiling in the usual way. - - [670] _Amer. J. Sci._ [iv.], 1912, ~34~, 214. - -Bourion[671] describes a method of separating the oxides by the action -of a mixture of hydrogen chloride and sulphur monochloride at a suitable -temperature. The ferric chloride which is formed sublimes, leaving -titanium dioxide unattacked. - - [671] _Compt. rend._ 1912, ~154~, 1229. - -For volumetric estimation of small quantities of titanium in solution, -colorimetric methods are generally employed. Addition of hydrogen -peroxide to such a solution gives an intense reddish-yellow colouration, -which is compared with the colourations obtained with solutions -containing known quantities of the element. Wells[672] finds that under -suitable conditions, an accuracy of about 2 per cent. is to be expected -with this method. Lehner and Crawford[673] find that in concentrated -sulphuric acid solution, thymol gives a red colouration which is at -least twenty-five times as intense as the colour given by hydrogen -peroxide, and they accordingly propose thymol as a suitable reagent for -the colorimetric estimation. Fenton[674] has shown that a very intense -colouration is obtained when a solution of a titanium salt is treated -with dihydroxymaleic acid; this reaction has been shown by Mellor[675] -to be well adapted for the colorimetric estimation and for the -estimation of titanium and vanadium together in a solution. - - [672] _Zeitsch. anorg. Chem._ 1911, ~70~, 395. - - [673] _J. Soc. Chem. Ind._ 1912, ~31~, 956. - - [674] _Trans. Chem. Soc._ 1908, ~93~, 1064. - - [675] _Abstr. Chem. Soc._ 1913, ~104~, ii. 627. - -The volumetric methods for the estimation of larger quantities require -complete reduction to the trivalent condition. This is best effected by -means of zinc and hydrochloric acid, or, where potassium permanganate is -to be used, by zinc and sulphuric acid. Precautions must be taken to -ensure that reduction is complete; an apparatus suitable for rapid -estimations has recently been described by Shimer and Shimer.[676] Where -potassium permanganate is employed (Pisani’s method), the iron must be -estimated separately by means of a standard solution of titanium -trichloride. Knecht and Hibbert[677] titrate directly, after reduction, -with a standard solution of a ferric salt, using potassium thiocyanate -as indicator; here no correction has to be applied for iron originally -present in the solution. The same advantage attaches also to the method -of titration by means of methylene blue,[678] a dye reduced to the -colourless leuco-base by salts of trivalent titanium, but not affected -by ferrous salts. - - [676] _J. Soc. Chem. Ind._ 1912, ~31~, 955. - - [677] _Ber._ 1903, ~36~, 1549. - - [678] See Hibbert, _J. Soc. Chem. Ind._ 1909, ~28~, 190. - - - - -INDEX - - - Absorption Spectra, ~148~ - - Acetate process, ~304~ - - Acetylacetone derivatives, ~135~ - - Actinium, 100 - - Aenigmatite, 8, 55 - - Aeschynite, 8, ~65~ - - Aldebaranium, 205 - - Allanite, 8, 36, ~39~, 91 - - Alshedite, 54 - - Alvite, 8, 59 - - Anatase, 8, ~78~ - - Ancylite, 8, 81 - - Anderbergite, 8, 49 - - Annerödite, 9, 61 - - Arc spectra, ~151~ - - Arfvedsonite, 9, 51 - - Arizonite, 9, 59 - - Arrhenite, 9, 70 - - Astrophyllite, 9, 55 - - Auer mantles, history of, ~270~ - - Auerbachite, 9, 31 - - Auerlite, 9, 51 - - - Baddeleyite, 10, ~75~ - - Bagrationite, 10, 45 - - Bastnäsite, 10, 81 - - Beckelite, 10, 51 - - Benitoite, 10, 55 - - Beryl, 102 - - Blomstrandine, 10, ~68~ - - Blomstrandite, 10, 71 - - Bodenite, 11, 42, 45 - - Bragite, 63 - - Brasilite, 76 - - Britholite, 11, 51 - - Bröggerite, 11, 73 - - Brookite, 11, ~79~ - - Bucklandite, 42 - - - Calciothorite, 11, 49 - - Calcite, 2, 38 - - Cappelenite, 11, 51 - - Carbides of rare earth group, ~120~ - - Carbonates of rare earth group, ~130~ - - Caryocerite, 12, 51 - - Cassiopeium, 205 - - Cassiterite, 3, 45, 46, 77 - - Castelnaudite, 12, 88 - - Cataplejite, 12, 51 - - Cathode luminescence, ~151~ - - Celtium, ~207~ - - Ceria, 111, 117, 118, ~161~ - - Ceric compounds, ~160~ - - Cerite, 1, ~30~ - - Cerium, atomic weight of, ~164~ - compounds, applications of, ~317~ - detection of, ~165~ - estimation of, ~166~ - group, history of, ~168~ - separation of, ~169~ - intermediate oxide of, 162 - metallic, ~115~ - nitrate, extraction from monazite of, ~284~ - separation of, ~156~ - - Cerous compounds, ~158~ - - Chalcolamprite, 12, 70 - - Chardonnet process, ~302~ - - Chlorides of rare earth group, ~121~ - - Chromates of rare earth group, ~129~ - - Churchite, 12, 80 - - Clamond mantles, ~268~ - - Cleveite, 13, 73 - - Cordylite, 13, ~80~ - - Cossyrite, 13 - - Cryptolite, ~84~ - - Cuprammonium process, ~303~ - - Crytolite, 13, 49 - - - Davidite, 13, 59 - - Delorenzite, 13, ~56~ - - Derbylite, 13, ~59~ - - Drummond light, ~267~ - - Dysanalyte, 14, 71 - - Dysprosium, ~199~ - history of, 195 - separation of, 196 - - - Edwardsite, 84 - - Elpidite, 14, 45 - - Endeiolite, 14, 70 - - Equivalent weight determination, ~153~ - - Erbium, atomic weight of, ~202~ - detection of, ~203~ - group, 199 - history of, 194, ~201~ - salts of, ~202~ - separation of, 196 - - Erdmannite, 14, 45 - - Eremite, 84 - - Erikite, 14, 51 - - Ethylsulphates of rare earth group, ~127~ - - Eucolyte, 14, ~50~ - - Eucolyte-Titanite, 54 - - Eucrasite, 15, 49 - - Eudialite, 15, ~50~ - - Europium, atomic weight of, 188 - compounds of, ~188~ - history of, 185 - - Euxenite, 15, 66, ~68~ - - Eytlandite, 60 - - - Fahnehjelm mantles, ~269~ - - Fergusonite, 15, 38, ~63~, 90 - - Ferrocyanides of rare earth group, ~123~ - - Ferro-titanium, ~326~ - - Florencite, 15, 51 - - Fluocerite, 15, 89 - - Fluorides of rare earth group, ~120~ - - Fluorspar, 2, 89, 102 - - Formates of rare earth group, ~133~ - - Freyalite, 16, 49 - - - Gadolinite, 1, 16, ~33~, 91 - - Gadolinium, atomic weight of, 190 - compounds of, ~190~ - detection of, 191 - history of, 184, ~189~ - - Geikielite, 16, 59 - - Gorceixite, 16, 88 - - Greenovite, 54 - - Gröthite, 26, 54 - - Guarinite, 16, 51 - - Gummite, 73 - - - Hainite, 16, 70 - - Halogen oxy-salts of rare earth group, ~123~ - - Harmatite, 10, 81 - - Helium ratio, 104, ~106~ - - Hellandite, 16, ~42~ - - Hiortdahlite, 17, ~51~ - - Hjelmite, 17, 64 - - Holmium, compounds of, ~201~ - history of, ~195~ - separation of, 196 - - Homilite, 17, 51 - - Hussakite, 17, 87 - - Hydrides of rare earth groups, ~116~ - - Hydrotitanite, 17, 59 - - Hydroxides of rare earth groups, ~116~ - - - Illuminating power of gas, 266 - of mantles, ~294~ - - Ilmenite, 17, ~57~, 90 - - Ilmenorutile, 17, 71 - - - Johnstrupite, 17, 55 - - - Kainosite, 18, 45 - - Karyocerite, 12 - - Kataplejite, 12, 51 - - Keilhauite, 18, ~52~ - - Kischtimite, 18, ~81~ - - Knopite, 18, 59 - - Kochelite, 18, 64 - - Koppite, 18, 64 - - - Lanthanite, 18, ~79~ - - Lanthanum, atomic weight of, ~173~ - compounds of, ~172~ - detection of, 173 - metallic, ~115~, 171 - separation of, ~170~ - - Lavenite, 19, 51 - - Lead, 105, ~107~ - - Lederite, 54 - - Leucosphenite, 19, 55 - - Leucoxene, 55 - - Lewisite, 19, 59 - - Lighting devices, ~315~ - - Ligurite, 54 - - Loranskite, 19, 64 - - Lorenzenite, 19, 55 - - Lutecium, ~205~ - - - Mackintoshite, 19, 79 - - Magnetic susceptibility, ~152~ - - Malacone, 19, 49 - - Mauzeliite, 20, 59 - - Melanocerite, 20, 51 - - Menaccannite, ~57~ - - Mengite, 84 - - Mesothorium, ~252~, 276 - - Metals of rare earth group, ~114~ - - Michaelsonite, ~14~ - - Microlite, 20, 64 - - Misch metal, ~115~, ~315~ - - Molengraafite, 20, 55 - - Monazite, 4, 20, ~82~ - sands, 83, ~90~ - technical treatment of, ~276~ - - Mosandrite, 20, 55 - - Muromontite, 20, 42, 45 - - - Naegite, 31, 45, ~49~ - - Narsarsukite, 21, 55 - - Neodymium, atomic weight of, ~179~ - detection of, ~180~ - metallic, 115, 177 - oxides, ~177~ - salts, ~178~ - - Neoytterbium, 206 - - Neptunite, 21, 55 - - Nernst lamp, ~320~ - - Nitrates of rare earth group, ~128~ - - Nitrides of rare earth group, ~116~ - - Nivenite, 21, 73 - - Nohlite, 21, 64 - - - Octahedrite, 8, ~78~ - - Oerstedite, 21, ~49~ - - Oisanite, 78 - - Orangite, 21, ~45~ - - Organic salts of rare earth group, ~133~ - - Orthite, 8, ~39~ - - Oxalates of rare earth group, ~131~ - - Oxides of rare earth group, 115, ~117~ - - - Parisite, 21, ~80~ - - Pauly process, ~303~ - - Perovskite, 14, 22, 59 - - Peroxides of rare earth group, ~117~ - - Pertitanates, ~235~ - - Phosphates of rare earth group, ~129~ - - Phthalates of rare earth group, ~134~ - - Picroilmenite, 16, ~59~ - - Pictite, 54 - - Pilbarite, 22, ~49~ - - Pitchblende, 22, ~72~ - - Platinocyanides of rare earth group, ~123~ - - Platinum mantles, ~268~ - - Plumboniobite, 22, ~62~ - - Polonium, 99 - - Polycrase, 22, ~66~ - - Praseodymium-- - atomic weight of, ~175~ - compounds of, ~174~ - detection of, 176 - history of, 168 - metallic, ~115~, 174 - separation of, ~170~ - - Priorite, 22, ~66~ - - Pseudobrookite, 22, 59 - - Pyrochlore, 23, 71 - - Pyromorphite, 101 - - Pyrophanite, 23, 59 - - Pyrophoric alloys, ~314~ - - - Radioactivity, ~99~ - - Radiothorium, 74, 99, ~253~ - - Ramie, mantles of, ~291~ - - Rare earth mixtures, examination of, ~147~ - - Rare earths-- - extraction of, from minerals, ~147~ - and periodic classification, ~135~ - - Retzian, 23, 88 - - Rhabdophane, 23, 88 - - Rhönite, 23, 55 - - Rinkite, 23, 55 - - Risörite, 23, 38, ~69~, 102 - - Rogersite, 24, 64 - - Rosenbuschite, 24, 55 - - Rowlandite, 24, 55 - - Rutile, 24, 45, ~77~, 90 - - - Samarium, atomic weight of, 182 - detection of, 183 - history of, ~168~ - metallic, ~115~, 181 - salts of, ~182~ - separation of, ~171~ - - Samarskite, 24, 38, ~60~, 91 - - Scandium, atomic weight of, ~217~ - chemical relations of, ~214~ - compounds of, ~215~ - detection of, ~218~ - history of, 194, ~213~ - occurrence of, ~3~ - separation of, ~186~ - - Schorlomite, 24, 55 - - Scovillite, 23, 88 - - Selenates of rare earth group, ~128~ - - Selenites of rare earth group, ~128~ - - Semelene, 54 - - Senaite, 24, 59 - - Silicofluorides of rare earth group, ~121~ - - Sipylite, 24, 39, ~63~ - - Spark spectra, ~150~ - - Sphene, 26, ~52~, 90, 107 - - Steenstrupine, 25, 51 - - Strüverite, 25, 71 - - Sulphates of rare earth group, ~124~ - - Sulphides of rare earth group, ~119~ - - Sulphites of rare earth group, ~127~ - - Synchisite, ~81~ - - - Tachyaphaltite, 25, 49 - - Tautolite, 42 - - Tengerite, 25, 81 - - Terbium, atomic weight of, ~192~ - detection of, 193 - group, chemical relations of, ~185~ - history of, ~184~ - separation of, ~186~ - history of, ~184~, 191 - salts of, 192 - - Thalénite, 25, ~43~, 102 - - Thiosulphates of rare earth group, ~127~ - - Thorianite, 25, ~73~, 107, 251 - - Thorite, 25, ~45~, 108, 251 - - Thorium, atomic weight of, ~262~ - chemical relations of, ~251~ - compounds of, ~254~ - detection of, ~263~ - estimation of, ~285~ - extraction of, 251, ~275~, 283 - group relations of, ~220~ - metallic, ~253~ - radiochemistry of, ~252~ - separation of, ~277~ - sulphate purification of, ~279~ - - Thorogummite, 26, 49 - - Thortveitite, 26, ~44~ - - Thulium, history of, ~194~, 203 - individuality of, ~204~ - salts of, ~204~ - separation of, 196 - - Titanates, ~234~ - - Titaniferous ironstone, ~57~ - - Titanite, 26, ~52~, 90 - - Titanium, atomic weight of, ~236~ - compounds for fixation of nitrogen, ~337~ - compounds of, in dyeing, ~333~ - compounds of divalent, ~225~ - compounds of trivalent, ~226~ - compounds of tetravalent, ~230~ - cyanonitride, ~224~ - detection of, ~236~ - electrodes, ~331~ - estimation of, ~338~ - group relations of, ~219~ - metallic, ~223~ - occurrence and extraction of, ~222~ - olivine, 26, 55 - steels, ~329~ - uses of, in metallurgy, ~327~, ~330~ - - Tritomite, 26, 51 - - Tscheffkinite, 26, 55 - - Tungsten, 1, 31 - - Turnerite, 83 - - Tyrite, 63 - - Tysonite, 26, 89 - - - Uhligite, 27, 59 - - Uraninite, 29, ~52~ - - Uranosphærite, 73 - - Urano-tantalite, 60 - - - Vasite, 42 - - Vietenghfiote, 27, 64 - - Viscose process, ~304~ - - - Warwickite, 27, 59 - - Weibyite, 27, 81 - - Wiikite, 27, ~70~ - - Wöhlerite, 28, 70 - - Wolframite, 2, ~214~ - - - Xenotime, 28, 45, ~86~, 90, 207 - - - Ytterbia, 1, 206 - - Ytterbite, 1, 33 - - Ytterbium, atomic weight of, 206 - detection of, 207 - history of, ~194~, 205 - salts of, ~206~ - separation of, 196, ~205~ - - Yttria, 1, 35, ~111~, 209 - - Yttrialite, 28, ~34~, 45 - - Yttrium, atomic weight of, ~211~ - detection of, ~212~ - group, history of, ~194~ - separation of, ~195~ - history of, 194, ~208~ - salts of, ~210~ - separation of, ~196~, 205 - - Yttrocerite, 28, ~88~ - - Ythrocrasite, 28, 56 - - Ythrofluirite, 28, ~89~ - - Yttrofluorite, 28, ~89~ - - Yttrogarnet, 28, 45 - - Yttrogummite, 28, 49 - - Yttroilmenite, 60 - - Yttrotantalite, 29, 62 - - Yttrotitanite, 18, ~52~ - - - Zircon, 29, 38, 45, ~47~, 90, 107 - - Zirconia, uses of, ~323~ - - Zirconium, atomic weight of, ~249~ - compounds of, ~249~ - detection of, ~242~ - estimation of, ~250~ - extraction of, ~239~ - group, relations of, ~219~, 240 - history of, ~238~ - industrial applications of, ~321~ - - Zirkelite, 29, 79 - - - PRINTED BY - SPOTTISWOODE AND CO. LTD., COLCHESTER - LONDON AND ETON - - - - - Transcriber’s Notes - - - Inconsistent and unusual spelling and hyphenation (including those of - proper and geographical names) have been retained, except as mentioned - below. - - Depending on the hard- and software used and their settings, not all - elements may display as intended. - - Lists of elements were printed both with and without separating commas - (for example, R´´ = Ca, Fe´´, Be and R´ = NH₄,K,Rb,Cs); these have not - been standardised. - - Pages 34, weighing 200 lb.: later (page 41) referred to as weighing - 300 lb. - - Some tables appear to use nm, others Å; this has not been - standardised. - - Page 181, table: 5923·35 may be an error; it is out of sequence. - - Page 200, table: 379·5 may be an error; it is out of sequence. - - Page 236, (NH₄)₂O₂,TiO₃,H₂O₂: as printed in the source document; the - final O₂ is probably an error. - - - Changes: - - Footnotes have been moved to under the paragraph in which they are - referenced; illustrations have been moved out of text paragraphs. - - Some obvious minor typographical and punctuation errors have been - corrected silently. - - Moh’s scale has been changed to Mohs’ scale, Guèrin and Guérin to - Guérin. Where there was a space between the number and the percent - sign, or between the degree sign and the C, this has been deleted for - the sake of consistency. - - Page vii: Blomstandine changed to Blomstrandine. - - Page 20, Monazite: Yttr = 1 4; changed to Yttr = 1-4; - - Page 26: Osterby changed to Österby. - - Page 46: Struverite changed to Strüverite as elsewhere. - - Page 87: Kraus and Heitinger changed to Kraus and Reitinger. - - Page 155: Footnote anchor [194] was missing in the source document, - and has been inserted at the end of the paragraph. - - - - - -End of the Project Gutenberg EBook of The Rare Earths, by S. I. 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