“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
18
The Platinum Metals in the Periodic
System
“The six know n platiniferous m etals , f r o m a
certain point o f view , m a y be rightly con ­
sidered as fo rm in g a separate and w ell-defin ed
group . ”
K \ K I . k \ K I . < ) \ 1( 11 M . M S . I 8 6 0
The gradual increase in the num ber of elements being discovered a n d isolated
during the early p a rt of the nineteenth century led to a n u m b er of attem pts at
their classification. As early as 1816 the great physicist A ndré M arie Ampère
(1775—1836), Professor of M athem atics an d M echanics at the École Polytechni­
que but at this stage of his career very interested in chemistry an d in the whole
concept of classification, put forward a scheme of ordering the elements that
would bring out “ the most num erous and essential analogies and be to
chemistry what the natural m ethods are to botany and zoology” (1). All the ele­
ments then known were classified into five groups, one of these being called the
“ Chrysides” , derived from the Greek word for gold, and including palladium ,
platinum, gold, iridium and rhodium . O sm ium , however, he grouped with
titanium. Some of the similarities between the p latinum metals were thus recog­
nised at this early date, but A m p è re ’s m ethod contained no num erical concept.
D o b e r e in e r ’s T riads
T h a t such a quantitative component was necessary was first recognised by J. W.
Dôbereiner who noticed in 1817 that the molecular weights for calcium oxide,
strontium oxide and barium oxide formed a regular series or triad with th a t of
strontium being the arithm etic m ean of the other two. Twelve years later he
published his paper on the Classification of the Elements in Poggendorff’s
Annalen der Physik und Chemie, curiously immediately following a n abridged
translation of W ollaston’s p a p e r on the production of m alleable platin u m given
to the Royal Society in 1828 (2). Expressing first his great interest in the atomic
weights of Berzelius, Dôbereiner again showed that w hen the elements were
arranged in groups of three resembling each other chemically the atomic weight
333
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
of the middle one was the m ea n of the other two. After discussing the halogens,
the alkaline earths and the g ro u p of sulphur, selenium a n d tellurium am ong
others, he tu rn e d to the sim ilarities between iron, nickel a n d cobalt and then to
the p latinum metals:
“ The interesting series of analogous metals that occur in native Platina, namely
Platinum, Palladium, Rhodium, Iridium, Osmium and Pluran, fall according to their
specific and atomic weights into two groups. To the first belong Platinum, Iridium
and Osmium, to the other Palladium, Rhodium and Pluran, which last corresponds
with osmium, as rhodium does with iridium and palladium with platinum” .
His Pluran, to which he referred in a footnote (“ T h e existence of Pluran is
however somewhat doubtful” ) w a s one of the supposed elements discovered by
O s a n n in 1827 in native p la tin u m from the Urals an d given th at n am e from the
two initial letters of Platinum a n d Urals. O nly in 1844 was the true sixth
m em ber of the group, ru th e n iu m , discovered by Klaus, as recorded earlier in
C h a p te r 12.
Very little was heard of D o b e re in e r’s triads. Not until 1853 in fact did any
serious notice a ppear to have b e e n taken of them, but in th at year J o h n Hall
Gladstone (1827-1902), a former student of T h o m a s G r a h a m and Liebig, then a
lecturer in chemistry at St. T h o m a s ’ H ospital in L ondon an d later Fullerian
Professor of Chemistry at the R o y a l Institution, published a p a p e r in The Philoso­
ph ical M agazine, O n the R elations between the Atomic W eights of Analogous
Elements. In the course of this he c o m m e n te d :
“ Who has failed to remark that the platinum group has double the atomic weights
of the palladium group” (3).
Four years later Ernst Lenssen, one of the young assistants in Professor
Fresenius’ analytical laboratory in W iesbaden, also speculated on the triads,
grouping the elements by their chem ical a n d physical characteristics and even
by the colour of their oxides (4) included one consisting of palladium , ruthenium
an d rhodium (in that order) a n d another com prising osmium , platin u m and
iridium, again incorrectly a rr a n g e d by their then atom ic weights, or rather the
equivalents, that he employed.
T h e S ch em es o f O d lin g an d N e w l a n d s
A more comprehensive scheme for the classification of the elements was also
published in 1857 by William O d lin g , at that time Professor of Chem istry at
G u y ’s Hospital in London. In this he arranged forty-nine elements into thirteen
groups of which the last contained the p latinum m etals a n d gold. H e wrote:
“ The propriety of associating gold with the platinum group is very questionable.
Palladium appears to present a relation of parity with rhodium and ruthenium,
platinum with iridium and possibly with osmium, though indeed many osmic reac­
tions are altogether special” (5).
D uring their work on the p la tin u m metals described in C h a p te r 15, Deville
334
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
W illiam O dling
1829-1921
T h e so n o f a L o n d o n d o c t o r . O d l i n g
entered
G u v 's
H o sp ita l
to st u d y
m edicine a n d ch em istry , becom ing a
d e m o n s t r a t o r in t h e l a t t e r s u b j e c t in
1850. A f t e r a p e r i o d o f st u d y u n d e r
G e r h a r d t in P a r i s h e w a s a p p o i n t e d a
lecturer
and
then
Professor
of
P r a c t i c a l C h e m i s t r y in 1856. T h e first
o f his s e v e ra l p a p e r s o n t h e c la s sif ic a ­
tion o f t h e e l e m e n t s a p p e a r e d a y e a r
l ater. In 1859 h e w as e l e c t e d a Fellow
o f th e R o y a l S o ciety a n d in t h e f o l lo w ­
ing y e a r h e a t t e n d e d t h e K a r l s r u h e
C o n g r e s s.
In
1868
he
succeeded
F a r a d a y as F u l l e r i a n P r o f e s s o r of
C h e m i s t r y at t h e R o y a l I n s t i t u t i o n ,
m oving
to
O xford
as
W aynflete
P r o f e s s o r o f C h e m i s t r y in 1872. In t h a t
y e a r h e m a r r i e d t h e d a u g h t e r of A l f r e d
S m e e , t h e s u r g e o n to t h e B a n k of
F n g lan d .
whose
w ork
on
the
e l e c t r o p l a t i n g of t h e p l a t i n u m m e t a l s
h a s b e e n d e s c r i b e d in C h a p t e r 1 1
and D ebray also emphasised the resemblances betw een these elements. I n 1859
they wrote:
“The family of the platinum metals has a particular character, completely apart
from the more or less natural families formed by the other metals. It is true that they
are not entirely analogous on every point, but they have their own character, a
common appearance that separates them, while from the point of view of a rational
classification one should separate them from the diverse families of elements” (6).
Odling returned to this subject later, revising an d extending his classification
in 1861 and again in 1864, but in the interval Karl Klaus presented a p a p e r on
the platinum metals to the Academy of Science in St. Petersburg in which he
also recognised them as a distinct group of elements (7):
“These metals may be arranged in two superimposed series, the superior
horizontal which I designate the principal series because the metals which constitute
it predominate in the various platinum ores. This series is characterised equally by an
elevated atomic weight and by almost the same specific gravity . . . The second
horizontal series contains the remainder of the platiniferous metals, which also
possess almost identical atomic and specific weights, but have in this respect but half
the quantities of the principal series”.
335
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
J o h n A le x a n d e r R e in a N e w la n d s
1837-1898
H o r n in L o n d o n of a S c o t t i s h f a t h e r
and an
Italia n m o th e r. N ew lands
jo in ed G a r ib a ld i's rev o lu tio n a ry m o v e ­
m e n t in I 8 6 0 , r e t u r n i n g in 18 63 to
study u n d e r H o f m a n n at th e Royal
C o lle g e o f C h e m i s t r y , l a t e r b e c o m i n g a
t e a c h e r o f c h e m i s t r y a n d t h e n in 1868
c h i e f c h e m i s t to a s u g a r r e f i n e r y . His
n u m e r o u s p a p e r s on t h e c la s sif ic a tio n
o f t h e e l e m e n t s w e r e r e c e i v e d with
s c e p t i c i s m , b u t h i s " L a w of O ctaves'*
w a s a n i m p o r t a n t if d e f e c t i v e f o r e r u n ­
n e r o f M e n d e l e e v *s P e r i o d i c S y s t e m
Klaus went on to show that th e metals vertically above one another in his
table resembled each other, the pairs ru th e n iu m an d osmium, rhodium and
iridium, and palladium and p la tin u m having identical reactions in the formation
of their compounds.
K l a u s ’s H o r iz o n ta l S e rie s
Principal Series
Secondary Series
Osmium
Ruthenium
Iridium
Rhodium
Platinum
Palladium
It will be seen that Klaus h a d his metals in the correct order as established
m uch later on.
In his famous Lecture on P latinum , given to the Royal Institution in
February 1861, Faraday clearly accepted these conclusions and quoted Klaus
almost verbatim (8).
O d lin g ’s revised and enlarged scheme of 1861 included fifty-seven elements
arranged in seventeen groups, the last two being very similar to those of Klaus (9),
336
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
and then in 1863 the first of a long series of papers by J. A. R. N ew lands
appeared in Chemical N ew s, followed by several more in the next three years (10).
In his final table of the elements, arranged numerically in the order of their
atomic weights, he pointed out that
“the numbers of analogous elements generally differ either by seven or by some mul­
tiple of seven; in other words members of the same group stand to each other in the
same relation as the extremities of one or more octaves in music . . . This relationship
I propose to provisionally term the Law of Octaves”.
Newlands was uncertain how to deal with the p latinum metals a n d he
achieved his arithm etical symm etry only by assigning one n u m b er to each of the
pairs rhodium a n d ruthenium in the earlier series a n d to p latinum and iridium
in the later, while he placed osmium alongside tellurium in another group. He
also predicted that another element should exist betw een iridium a n d rhodium
and another between palladium and platinum . U nfortunately for N ew lands the
Chemical Society declined to publish his paper, Odling, later the President,
explaining that they “ m ade it a rule not to publish papers of a purely theoretical
n a tu re ” .
Newlands continued to interest himself in arranging the elements so as to
emphasise the family relationships, assigning consecutive atomic or “ o r d in a l”
numbers to them and leaving blanks for elements as yet to be discovered, a n d in
a small book he produced in 1884 he claimed with some justification to have
been the first to publish a list of the elements in the order of their atom ic weights
and to have described the periodic law (11).
M eanwhile in 1864 Odling, probably unaw are of N e w la n d s’ later publica­
tion, contributed a p a per “ O n the Proportional N um bers of the E le m e n ts” to the
Quarterly Jou rn al o f Science in which he listed sixty-one elements in increasing
order of atomic weight (12). In this he gave rhodium , ru thenium an d palladium
in that order an d then platinum , iridium and osmium.
T h e K a r lsru h e C ongress
T he accuracy of the atomic weights so far determ ined was in grave doubt and
the subject of much controversy. Some values were only one half of their now
established figures while some were twice as great. Friedrich W ohler had com ­
plained that “ the confusion can be tolerated no longer” . From this state of chaos
order was restored by the well-known p a p e r from Stanislao Cannizzaro,
(1826-1910), Professor of Chem istry at Genoa, given at the K arlsruhe Congress
in 1860 (13). This famous gathering of more th a n 120 chemists, the first inter­
national scientific conference, was proposed by August Kekule a n d some of his
colleagues to secure more precise definitions of the concepts of atom s and
molecules a n d to bring uniformity into the values of atomic weights. William
Odling, one of the very few who ha d already read C a n n iz z a ro ’s p a p e r was
among the signatories calling this meeting and he was present for the discussion.
337
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
Earlier he had studied chem istry in Paris u n d e r G e rhardt, h a d translated
L a u re n ts’ M ethode de C him ie into English in 1855, and supported their unitary
theory, the atomic weight to b e taken as the smallest quantity of a n element
present in the molecular weight of any of their compounds. But it was C a n ­
nizzaro, whose paper, a rep rin t of a n earlier contribution given in 1858, was
distributed by his colleague A ngelo Pavesi, Professor of Chem istry at Pavia, after
the close of the meeting that settled the whole problem of atomic weights based
upon the earlier proposals of G e r h a rd t a n d Laurent. H alf a century of confusion
was cleared up and it was now possible to ascribe the correct atom ic weights to
all the known elements.
L othar M e y e r and M e n d e l e e v
Among those attending the K a rlsru h e Congress was Julius L othar Meyer, at
that time Professor of C h e m istry at Breslau, a n d he recorded later how on
reading C annizzaro’s p a per d u rin g his retu rn jo u rn e y “ the scales fell from my
eyes, doubt vanished, an d was replaced by a feeling of peaceful c e rtain ty ” .
W hen preparing a text-book M e y e r was thus able to take account of the
numerical relationships betw een the elements and in his Die M odernen
J u li u s L o th a r M ey er
1 8 3 0 -1 8 9 5
A n a t i v e o f t h e s m a ll t o w n o f V a r e l
n e a r O l d e n b u r g in n o r t h G e r m a n y ,
M e v e r w as f a r f r o m r o b u s t as a c h ild
a n d w as giv en a n o u t - d o o r e d u c a t i o n
u n d e r t h e h e a d g a r d e n e r to t h e D u k e o f
O l d e n b u r g . H e b e g a n his h i g h e r e d u c a ­
tio n a t Z ü r i c h a n d t h e n t r a n s f e r r e d to
W ü r z b u r g . A f t e r g r a d u a t i o n he w e n t to
H e i d e l b e r g to s t u d y u n d e r B u n s e n a n d
K i r c h h o f f a n d in 18 64 p u b l i s h e d his
b o o k on t h e m o d e r n t h e o r i e s of
c h e m i s t r y , this c o n t a i n i n g a t a b l e of
m o st o f t h e e l e m e n t s a r r a n g e d in o r d e r
o f t h e i r a t o m i c w eigh ts . H e b e c a m e
P rofessor
of
C hem istry
in
the
T e c h n i s c h e H o c h s c h u l e at K a r l s r u h e in
1869 a n d in 1876 a c c e p t e d a s i m i l a r
c h a i r in t h e I n i v e r sity o f T ii b i n g e n . In
1 88 2 h e a n d M e n d e l e e v w e r e join tly
a w a r d e d t h e Davy M e d a l by t h e R o yal
S o c i e t y f o r t h e i r d e v e l o p m e n t of t h e
p e r i o d i c system
338
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
T heorien der Chemie, written in 1862 but not published until 1864, he included
a table of most of them (14). Here he placed correctly the three lighter m em bers
of the platinum group, ruthenium , rh o d iu m and palladium , b u t wrongly gave
the heavier three in the order platinum , iridium an d osmium, an error th a t he
was later to rectify.
In the m eantime, however, the most clear and comprehensive tre a tm e n t of
the elements and their classification was devised, as every chemist knows, by the
outstanding genius D m itri Ivanovich Mendeleev, the great R ussian scientist
whose nam e has ever since been firmly associated with the Periodic Table.
Mendeleev had studied at St. Petersburg an d he ha d been m ore th a n fortunate
in his teachers. T h e senior of these, Professor Nikolai Nikolaevich Zinin
(1812-1880) had travelled widely in western Europe, spending a year with
Liebig at Giessen an d returning to the University of K az a n where in 1841 he had
been a close colleague of Klaus before being called to St. Petersburg in 1847. He
accepted the new concepts of G erhardt and Laurent, the first to do so in Russia,
a nd he attended the K arlsruhe Congress in 1860. M endeleev’s other mentor,
who became closely attached to his brilliant student and gave him private
lessons during a period of illness, was Professor Aleksyei Andreivich
Voskressenskii (1809-1880) who ha d also spent some time w ith Liebig a n d who
was affectionately known to his students as “ the grandfather of Russian
chem istry” . He was also a disciple of G e rh a rd t and Laurent. Mendeleev, after
graduating, visited Paris to study u n d e r Victor R egnault and then spent a period
in Heidelberg where he opened a private laboratory. It was from there that he
travelled to K arlsruhe and his appreciation of those discussions is shown in a
letter he wrote to Voskressenskii th at was published in the St. Petersburg
Gazette.
This began:
“The chemical congress just ended in Karlsruhe produced such a remarkable
effect on the history of our science that I consider it a duty, even in a few words, to
describe all the sittings of the congress and the results that it reached”.
After giving a brief account of these discussions he c o n c lu d e d :
“ Cannizzaro spoke heatedly, showing that all should use the same new atomic
weights. There was no vote on the question, but the great majority took the side of
Cannizzaro”.
Mendeleev had devoted long years to the accum ulation of evidence for his
developing ideas on the classification of the elements, carrying out hun d red s of
experiments, reading widely in the literature an d corresponding with chemists
throughout Europe to collect appropriate data. All this information, on their
physical an d chemical properties, on the nature of their com binations a n d o n the
isomorphism of their compounds, was then inscribed on to small white cards
which he arranged until he was satisfied with their sequence. Early in 1869 he
distributed privately a pam phlet entitled “ A n Experim ental System of the Ele­
ments based on their Atomic W eights and Chem ical Analogies” , and then in the
339
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
following M arch, at a meeting o f the R ussian Chem ical Society which he had
done so m uch to organise in the previous year, a n d with Zinin presiding, a paper
from Mendeleev was read by his friend a n d colleague Professor Nikolai M enschutkin because the author had been taken ill. This was published in the first
volume of the Society’s tra nsactions (15), an d was briefly referred to in the
G e rm a n periodicals, giving their readers some indication of M endeleev’s ideas.
It was not, however, a complete periodic table as we know it b u t rath e r a p re ­
liminary study in which he m erely a rranged the elements in six colum ns and, as
he later emphasised, he was u n a w a re of the publications of M eyer and
Newlands a n d only of O d lin g ’s first com m unication of 1857 an d Lenssen’s even
earlier work.
As with his predecessors, M endeleev had difficulties with the p latinum group
of metals on account of their close similarity and the very small differences
in their atomic weights as th en determ ined. In this first system he arranged
them:
R h 104.4
Pt
197.4
Ru 104.4
Ir
198
O s 199
Pd 106.6
In a second paper read to a meeting of R u ssian scientists in M oscow in
August 1869, “ O n the Atomic V olum e of Simple Bodies” , (16), he produced a
clearer table, a prototype of his final version, in which he showed the eighth
group in the same order as before but he now assum ed the presence of an empty
period between the ru thenium a n d the osm ium groups.
T h e n in 1870 L othar M eyer contributed a p a p e r to Liebig’s Annalen, “ T h e
N a tu re of the Chemical E lem ents as a F u n c tio n of their Atomic W e ig h ts” , (17)
in which he arranged the p la tin u m metals in their correct order but with some
uncertainty:
Ru 103.5
O s 198.6?
R h 104.1
Ir
196.7
Pd 106.2
Pt
196.7
He commented:
“ To obtain this arrangement, some few of the elements whose atomic weights
have been found to be nearly equal, and which have probably not been very carefully
determined, must be rearranged somewhat, Os before Ir and Pt, and these before Au.
Whether this reversal of the series corresponds to the properly determined atomic
weights must be shown by later researches” .
Partly arising from this p a p e r of M e y e r ’s, Mendeleev published a further
account of his system a year later, and this was translated in full in the Annalen
(18). R unning to almost a h u n d r e d pages in the G e rm a n version, this gave a
m uch clearer and more com prehensive description of his periodic system - the
first time he actually used the p h r a s e - a n d dealt at length not only with the
properties of the elements but also with their com pounds. M ore courageous than
340
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
I> jn n a I.
rp jn n » 11.
r |iju n a HI-
rpjnn»
IV.
r |i j o n t V.
5* |
-
i«
K =39
(Ouz=63)
3 “
R b=85
i l l
5 j l
i l l
B *= 9,4
N i= 2 3
P i n 1-i
-
i f f
L i= 7
-
M
6-1
(**-=106)
C*=133
r p jn n a VII.
r p ja n * V III.
n rfja I,
1
H =1
Tat>a*teeaie u e MCHru.
Tpinn* VI.
-= 4 4
LU—»11
Ba—137
Ti=5»>?
(?Y t= 8 8 ?)
V=S1
8=31
Se=78
N b -9 4
Sn=118
F e — 5«,
Co=69,
N i= 5® , C u = 6 3
Br=8<)
-= lttl
Mu—»6
T e * _ l 28?
Sb=132
C 1=36,4
M n=M
¡C r=32
A c = 75
-= 7 2
Zrrz90
la =113
- =137
F=19
0=1«
P=31
- =_68
Z n= 6ft
S r z 87
H = l.
A l= 2 7 ,3
■«=*4
C a=40
C=12
B—11
R n = 1 0 4 ,R u = 1 0 4 ,
P d = H » 4 ,A f= l0 8
J — 127
C —-I38?
-
1
:::
ill - 9-"
hi
111
-
B ucuiai
HW>
-
—
T«=182
-
0 » = lt* 9 ? ,Ir= 1 9 8 ? ,
1*1=197, Aii = 1 9 7
W - 184
r
(A n = J 9 7 j
H|T=*Jf.
T l= 2 0 4
Bi=2U8
P b = * l7
T h r r 132
-
-
-
-
L’r = 2 4 0
—
c o jh h m
OBIICb.
Bucioee
ao*opoxnoe coejaaeine.
K *0
R’O* a j m KO
R*0*
RH)‘ a j a HO*
«»O '
R’O- m
i
RWI
K'O’
11*0-
iij«
RO*
i
(RH*?)
RH‘
RH*
RH*
RH
T h e r e v i s e d a n d c o m p r e h e n s i v e P e r i o d i c T a b l e p u b l i s h e d by M e n d e l e e v in t h e J o u r n a l
of t h e R u s s i a n C h e m i c a l S o ciety in 1871. T h e p l a t i n u m m e t a l s w e r e n o w p l a c e d in t h e i r
c o r r e c t o r d e r in G r o u p V I I I , a l t h o u g h this a ls o i n c l u d e d c o p p e r , s i l v e r a n d gold. A s p a c e
was left fo r a s yet u n d i s c o v e r e d m e m b e r s o f t h e p l a t i n u m g r o u p b e t w e e n t h e l i g h t e r a n d
t h e h e a v i e r t r i a d s a n d t h e a t o m i c w e i g h t s w e r e g iv e n o nly in r o u n d fig u res b e c a u s e of
M e n d e l e e v 's u n c e r t a i n t y a b o u t t h e i r a c c u r a c y
Lothar Meyer, he ascribed different atom ic weights to a n u m b e r of elements,
based solely upon their chemical analogies, calling for new determ inations to be
made. In the case of the three heavier platinum metals he wrote:
“Three elements stand in the system in succession between W = 184 and
Hg = 200. Their atomic weights are actually smaller than W, but the succession does
not correspond to expectations, for in considering that Os, Ru, Fe are similar, but
that Ru and Fe have smaller atomic weights than Pd and Ni, it is to be expected that
the atomic weight of Os is smaller than that of Pt, and that Ir, standing between Pt
and Os, has a middle value of atomic weight. Moreover, the inaccuracy of the atomic
weight determinations of the Pt metals is readily understood, not simply because their
separation from one another is difficult but also because their compounds that have
been used for atomic weight determinations are not of great stability”.
M endeleev’s table of 1871 is reproduced here from the original R ussian
version. It will be seen th at in addition to iron, cobalt an d nickel an d to the
platinum metals he had included copper, silver and gold in G roup V III but had
left alternative positions for them in G roup I, an d that, unaw are of most of the
rare earth elements, he ha d again left gaps for an extra series betw een the two
341
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
K a r l F r i e d r i c h O tto S e u b e r t
185 1-1 921
T h e son of a P ro fes so r at the K a r ls r u h e
T e c h n i s c h e H o c h s c h u l e , S e u b e r t first
stu d ied p h a rm a c y th e re a n d then
t u r n e d to c h e m i s t r y , s e r v i n g f o r s e v e r a l
y e a r s as a s s i s t a n t to L o t h a r M e y e r a n d
a c c o m p a n y i n g h i m to B r e s l a u a n d
t h e n to T ü b i n g e n o v e r a p e r i o d o f
t w e n t y y e a r s a n d s u c c e e d i n g h i m as
P r o f e s s o r . H i s d o c t o r a l t h e s is w as on
t h e a t o m i c w e i g h t o f i r i d i u m a n d he
w e n t 011 to r e - d e t e r m i n e t h e a t o m i c
w e i g h t s o f all t h e o t h e r p l a t i n u m
m e t a l s , c o n f i r m i n g t h e o r d e r in w h i c h
M endeleev had placed them
platinum metal triads. This h a d the inevitable result of pro m p tin g the re­
exam ination of native platinum for the a p parently missing elements and led to a
n um ber of “ discoveries” th at will be referred to a little later. Also, as is well
known, he successfully predicted from a knowledge of their adjacent elements all
the essential properties of as yet undiscovered elements, later to be identified as
germ anium , scandium, gallium, r h e n iu m and technetium.
In this table Mendeleev se p a ra te d th e elements into their m ain and sub­
groups, while he also confined his atomic weights to round num bers as he could
not be sure of their accuracy. H is predictions about the correct order for the
platinum metals were fully confirm ed a few years later by Karl Seubert
(1851-1921), a student and later a colleague of L othar M e y e r ’s at Tiibingen.
Seubert also distrusted some o f the old values a n d set about their re­
determination, arriving at the following arrangem ent a n d so confirming
M endeleev’s views (19):
Ru 101.4
R h 102.7
Pd 106.35
Os 190.3
Ir
192.5
Pt
194.3
342
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
S om e S p u rio u s P la tin u m M etals
Several supposedly new elements of the platin u m group were claim ed before the
publication of M endeleev’s Periodic Table, but the gaps he left, as already
mentioned, led to further claims for the isolation of further m em bers of the
group. In 1877 Sergius K ern of the Obouchoff Steel W orks in St. Petersburg
wrote to Chemical N ew s that he h a d “ perceived the presence of a new metal of the
platinum group which has been called by me davyum in honour of the great
English chemist Sir H u m p h ry D a v y ” (20). This claim was investigated in 1898
by Professor J. W. Mallet, a n Irish chemist who ha d settled in Am erica to
become Professor of Chem istry at the University of Virginia, an d who thought
this m ight indeed be a m em ber of the missing triad of p latinum metals. W hile he
was able to confirm K e r n ’s experimental observations, he quickly showed that
the new m etal was merely
“a mixture of iridium and rhodium with a little iron, and hence that we have not yet
reason to believe in the existence of a third group of platinum metals” (21).
A further “ discovery” was claimed by a French chemist, A ntony G u y a rd in
1879:
“ Some years ago, about 1809, I discovered in some commercially fabricated
platinum from Russian mineral a new member of the platinum group to which I give
the name of Ouralium to commemorate its origin” (22).
T h e atomic weight was given as 187.25, its specific gravity as 20.25 a n d its
ductility was said to be greater th a n that of platinum , but the experim ental work
was of a very low order and ouralium was again almost certainly a m ixture of
platinum with some iridium an d rhodium . T h e se two fallacious discoveries,
together with several others, were reviewed in m ore detail by Dr. W. P. Griffith
in 1968 (23).
T h e M o d e r n P e r io d ic T a b le
Mendeleev continued for the rem ainder of his life to take a n active interest in his
Periodic Law and used it as a base in his famous text-book, T h e Principles of
Chemistry, first published in Russia in 1869 and in m any later editions, with an
English translation in 1891 a n d G e rm a n an d French versions a few years later.
His chapter on the platinum metals opens with a statem ent of “ the naturalness
of the tra nsition” from zirconium, niobium an d m olybdenum to silver, cadm ium
and iridium through ruthenium , rhodium and palladium , and similarly from
tantalum and tungsten through osmium, iridium a n d p latin u m to gold and
mercury. This is followed by an account of the chemistry of the platinum metals
that would have been creditable to an a u th o r m any years later, as for th at m atte r
would the whole of the book.
But it was not until the discovery of the electron by Sir J . J. T h o m s o n in 1879
and then M oseley’s work on the X -ray spectra of the elements th at led to the
concept of atomic n um ber ju s t before his death in 1915 in the E uropean W ar
that a sound theoretical basis could be established for the periodic system.
343
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
The Platinum Metals and their Neighbours
in the Periodic Table
Group VIA
G roup VIIA
G roup VIII
G roup IB
First long period
C r 24
M n 25
F e 26 C o 27 N i 28
Cll 29
Second long period
M o 42
T c 43
R u 44 R h 45 P d 46
A g47
T h ird long period
w74
R e 75
0S76 Ir 77 Pt78
Au 79
T h e part of the m odern ta b le in which the platin u m metals occur is
reproduced above with their a to m ic num bers, this including of course rhenium
discovered in 1925 and p redicted by Mendeleev as dri-m anganese, and
technetium, his eka-manganese, discovered only in 1937 in the b o m b a rd m e n t of
m olybdenum by deuterons in a cyclotron. J u s t as Mendeleev emphasised, the
greatest similarities are found in the vertical groups; there is a strong
resemblance between ru thenium a n d osmium, betw een rhodium an d iridium,
a n d between palladium and p latin u m . At the same tim e there are obvious
analogies in the horizontal series, betw een for example palladium an d silver and
betw een platinum and gold, w hile ru th e n iu m a n d osm ium m ore closely
resemble technetium a n d rh enium , or in certain respects m olybdenum and
tungsten, th a n they do iron. R h o d iu m an d iridium are m ore closely allied to
cobalt than to any other m etal, while p latinum and p a lladium have close
analogies with nickel.
In the two p latinum metal tria d s the hardness a n d m echanical strength
decrease from left to right a n d a r e greater in the second triad th a n in the first.
R u th e n iu m and osmium, both close-packed hexagonal in crystal structure are
brittle although they can be fabricated with difficulty at high tem peratures,
while palladium and platinum faced-centred cubic metals, are soft and readily
workable in the cold. A review of these similarities in properties and of the
relevant chemical properties of t h e group was contributed some years ago by the
w riters’ colleague A. R. Powell (24).
344
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
R efe re n c es fo r C h a p t e r 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
A. M. Ampère, Ann. C h im , 1816, 1, 295-308; 2, 5-32
J. W. Dobereiner, Ann. Phys. ( Poggendorff), 1829, 15, 301-307
J. H. Gladstone, Phil. M ag., 1853, 5, 313—320
E. Lenssen, Ann. Chem. ( Liebig), 1857, 103, 121-131; 104. 177-184
W. Odling, Phil. M ag., 1857, 13, 422-^39; 480-497
H. Sainte-Claire Deville and H. Debray, Ann. Chim., 1859, 56, 385-389
C. Claus, J . prakt. Chem., 1860, 79, 28-59; 80, 282-317; Chem. News, 1861, 3,
194-195; 257-258
M. Faraday, A Lecture on Platinum, bound with The Chemical History of a
Candle, London, 1861, 173-204; Chem. News, 1861, 3, 136-141
W. Odling, A Manual of Chemistry, Part 1, London, 1861, 3
J. A. R. Newlands, Chem. News, 1863, 7, 70-72; 1864, 10, 59-60; 94-95; 1865, 12.
83
J. A. R. Newlands, On the Discovery of the Periodic Law, London, 1884
W. Odling, Q_.J. Sci., 1864, 1, 642-648
S. Cannizzaro, Il Nuovo Cimento, 1858, 7, 321—366; English translation in Alembic
Reprint 18; for an account of the Karlsruhe Congress see C. de Milt, J . Chem. Ed.,
1951, 28, 421—425
J. L. Meyer, Die modernen Theorien der Chemie, Breslau, 1864
D. I. Mendeleev, ^ [hur. Russ. Khim. Obshch., 1869, 1, 60-77
D. I. Mendeleev, Proc. 2nd Meeting Scientists, 23 Aug, 1869, 62-71
J. L. Meyer, Ann. Chem. ( Liebig), 1870, Supp. VII, 354—364
D. I Mendeleev, %hur. Russ. Khim. Obshch., 1871, 3, 25—56; Ann. Chem. ( Liebig), 1871,
Supp. VIII, 133-229
K. Seubert, Ann. Chem. ( Liebtg), 1891, 26 1, 272-279
S. Kern, Chem. News, 1877, 36, 4; 114-115; 164
J . W. Mailet, Am . C hem .J., 1898, 20, 776
A. Guyard, M oniteur Scientifique, 1879, 9, 795-797
W. P. Griffith, Chemistry in Britain, 1968, 4, 430^134
A. R. Powell, Platinum M etals Rev., 1960, 4, 144-149
345
© 1982 Johnson Matthey
“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt
H e n r i L o u is L e C h a te lie r
1850-1936
Born in Paris. I,e Chatelier spent some tim e u n d er Sainte-Claire Deville
at the Ecole Normale b ut his education was interrupted by the
F ranco/Prussian W ar. I.ater he studied at the Ecole des Mines and
becam e a mining engineer but in 1877 he retu rn ed there to teach
chemistry, being appointed Professor ten years later. He was the first to
employ a platinum against rhodium -platinum alloy therm ocouple, so
initiating a reliable means of determ ining high tem peratu res
© 1982 Johnson Matthey