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.