The Platinum Metals in the Periodic System

“A History of Platinum and its Allied Metals”, by Donald McDonald and Leslie B. Hunt

“The six known platiniferous metals, from a certain point of view, may be rightly con sidered as forming a separate and well-defined group.” K \ K I. k \KI.<)\ 1(11 M. M S. I860

The gradual increase in the number of elements being discovered and isolated during the early part of the nineteenth century led to a number of attempts at their classification. As early as 1816 the great physicist André Marie Ampère (1775—1836), Professor of Mathematics and Mechanics at the École Polytechni que but at this stage of his career very interested in chemistry and in the whole concept of classification, put forward a scheme of ordering the elements that would bring out “the most numerous and essential analogies and be to chemistry what the natural methods 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. Osmium, however, he grouped with titanium. Some of the similarities between the platinum metals were thus recog nised at this early date, but Ampère’s method contained no numerical concept.

Dobereiner’s Triads That 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 that of strontium being the arithmetic mean 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 an abridged translation of Wollaston’s paper on the production of malleable platinum given to the Royal Society in 1828 (2). Expressing first his great interest in the atomic weights of Berzelius, Dôbereiner again showed that when the elements were arranged in groups of three resembling each other chemically the atomic weight

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of the middle one was the mean of the other two. After discussing the halogens, the alkaline earths and the group of sulphur, selenium and tellurium among others, he turned to the similarities between iron, nickel and cobalt and then to the platinum 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 (“The existence of Pluran is however somewhat doubtful”) was one of the supposed elements discovered by Osann in 1827 in native platinum from the Urals and given that name from the two initial letters of Platinum and Urals. Only in 1844 was the true sixth member of the group, ruthenium, discovered by Klaus, as recorded earlier in Chapter 12. Very little was heard of Dobereiner’s triads. Not until 1853 in fact did any serious notice appear to have been taken of them, but in that year John Hall Gladstone (1827-1902), a former student of Thomas Graham and Liebig, then a lecturer in chemistry at St. Thomas’ Hospital in London and later Fullerian Professor of Chemistry at the Royal Institution, published a paper in The Philoso phical Magazine, On the Relations between the Atomic Weights of Analogous Elements. In the course of this he commented: “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 Wiesbaden, also speculated on the triads, grouping the elements by their chemical and physical characteristics and even by the colour of their oxides (4) included one consisting of palladium, ruthenium and rhodium (in that order) and another comprising osmium, platinum and iridium, again incorrectly arranged by their then atomic weights, or rather the equivalents, that he employed.

The Schemes of Odling and Newlands A more comprehensive scheme for the classification of the elements was also published in 1857 by William Odling, at that time Professor of Chemistry at Guy’s Hospital in London. In this he arranged forty-nine elements into thirteen groups of which the last contained the platinum metals and gold. He 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). During their work on the platinum metals described in Chapter 15, Deville

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William Odling 1829-1921 The son of a London doctor. Odling entered Guv's Hospital to study medicine and chemistry, becoming a demonstrator in the latter subject in 1850. After a period of study under Gerhardt in Paris he was appointed a lecturer and then Professor of Practical Chemistry in 1856. The first of his several papers on the classifica tion of the elements appeared a year later. In 1859 he was elected a Fellow of the Royal Society and in the follow ing year he attended the Karlsruhe Congress. In 1868 he succeeded Faraday as Fullerian Professor of Chemistry at the Royal Institution, moving to Oxford as Waynflete Professor of Chemistry in 1872. In that year he married the daughter of Alfred Smee, the surgeon to the Bank of Fngland. whose work on the electroplating of the platinum metals has been described in Chapter 1 1

and Debray also emphasised the resemblances between these elements. In 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 and extending his classification in 1861 and again in 1864, but in the interval Karl Klaus presented a paper 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”.

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John Alexander Reina Newlands 1 8 3 7 -1 8 9 8 Horn in London of a Scottish father and an Italian mother. Newlands joined Garibaldi's revolutionary move ment in I860, returning in 1863 to study under Hofmann at the Royal College of Chemistry, later becoming a teacher of chemistry and then in 1868 chief chemist to a sugar refinery. His numerous papers on the classification of the elements were received with scepticism, but his "Law of Octaves'* was an important if defective forerun ner of Mendeleev *s Periodic System

Klaus went on to show that the metals vertically above one another in his table resembled each other, the pairs ruthenium and osmium, rhodium and iridium, and palladium and platinum having identical reactions in the formation of their compounds.

Klaus’s Horizontal Series

Principal Series Osmium Iridium Platinum Secondary Series Ruthenium Rhodium Palladium

It will be seen that Klaus had his metals in the correct order as established much later on. In his famous Lecture on Platinum, given to the Royal Institution in February 1861, Faraday clearly accepted these conclusions and quoted Klaus almost verbatim (8). Odling’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),

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and then in 1863 the first of a long series of papers by J. A. R. Newlands appeared in Chemical News, 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 platinum metals and he achieved his arithmetical symmetry only by assigning one number to each of the pairs rhodium and ruthenium in the earlier series and to platinum and iridium in the later, while he placed osmium alongside tellurium in another group. He also predicted that another element should exist between iridium and rhodium and another between palladium and platinum. Unfortunately for Newlands the Chemical Society declined to publish his paper, Odling, later the President, explaining that they “made it a rule not to publish papers of a purely theoretical nature”. Newlands continued to interest himself in arranging the elements so as to emphasise the family relationships, assigning consecutive atomic or “ordinal” numbers to them and leaving blanks for elements as yet to be discovered, and 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 atomic weights and to have described the periodic law (11). Meanwhile in 1864 Odling, probably unaware of Newlands’ later publica tion, contributed a paper “On the Proportional Numbers of the Elements” to the Quarterly Journal of Science in which he listed sixty-one elements in increasing order of atomic weight (12). In this he gave rhodium, ruthenium and palladium in that order and then platinum, iridium and osmium.

The Karlsruhe Congress The accuracy of the atomic weights so far determined 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 Wohler had com plained that “the confusion can be tolerated no longer”. From this state of chaos order was restored by the well-known paper from Stanislao Cannizzaro, (1826-1910), Professor of Chemistry at Genoa, given at the Karlsruhe Congress in 1860 (13). This famous gathering of more than 120 chemists, the first inter national scientific conference, was proposed by August Kekule and some of his colleagues to secure more precise definitions of the concepts of atoms and molecules and to bring uniformity into the values of atomic weights. William Odling, one of the very few who had already read Cannizzaro’s paper was among the signatories calling this meeting and he was present for the discussion.

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Earlier he had studied chemistry in Paris under Gerhardt, had translated Laurents’ Methode de Chimie into English in 1855, and supported their unitary theory, the atomic weight to be taken as the smallest quantity of an element present in the molecular weight of any of their compounds. But it was Can nizzaro, whose paper, a reprint of an earlier contribution given in 1858, was distributed by his colleague Angelo Pavesi, Professor of Chemistry at Pavia, after the close of the meeting that settled the whole problem of atomic weights based upon the earlier proposals of Gerhardt and Laurent. Half a century of confusion was cleared up and it was now possible to ascribe the correct atomic weights to all the known elements.

Lothar Meyer and Mendeleev Among those attending the Karlsruhe Congress was Julius Lothar Meyer, at that time Professor of Chemistry at Breslau, and he recorded later how on reading Cannizzaro’s paper during his return journey “ the scales fell from my eyes, doubt vanished, and was replaced by a feeling of peaceful certainty”. When preparing a text-book Meyer was thus able to take account of the numerical relationships between the elements and in his Die Modernen

Julius Lothar Meyer 1830-1895 A native of the small town of Varel near Oldenburg in north Germany, M ever was far from robust as a child and was given an out-door education under the head gardener to the Duke of Oldenburg. He began his higher educa tion at Zürich and then transferred to Würzburg. After graduation he went to Heidelberg to study under Bunsen and Kirchhoff and in 1864 published his book on the modern theories of chemistry, this containing a table of most of the elements arranged in order of their atomic weights. He became Professor of Chemistry in the Technische Hochschule at Karlsruhe in 1869 and in 1876 accepted a similar chair in the I niversity of Tiibingen. In 1882 he and Mendeleev were jointly awarded the Davy Medal by the Royal Society for their development of the periodic system

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Theorien 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 members of the platinum group, ruthenium, rhodium and palladium, but wrongly gave the heavier three in the order platinum, iridium and osmium, an error that he was later to rectify. In the meantime, however, the most clear and comprehensive treatment of the elements and their classification was devised, as every chemist knows, by the outstanding genius Dmitri Ivanovich Mendeleev, the great Russian scientist whose name has ever since been firmly associated with the Periodic Table. Mendeleev had studied at St. Petersburg and he had been more than fortunate in his teachers. The senior of these, Professor Nikolai Nikolaevich Zinin (1812-1880) had travelled widely in western Europe, spending a year with Liebig at Giessen and returning to the University of Kazan 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 Gerhardt and Laurent, the first to do so in Russia, and he attended the Karlsruhe Congress in 1860. Mendeleev’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 had also spent some time with Liebig and who was affectionately known to his students as “the grandfather of Russian chemistry”. He was also a disciple of Gerhardt and Laurent. Mendeleev, after graduating, visited Paris to study under Victor Regnault and then spent a period in Heidelberg where he opened a private laboratory. It was from there that he travelled to Karlsruhe and his appreciation of those discussions is shown in a letter he wrote to Voskressenskii that 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 concluded: “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 accumulation of evidence for his developing ideas on the classification of the elements, carrying out hundreds of experiments, reading widely in the literature and corresponding with chemists throughout Europe to collect appropriate data. All this information, on their physical and chemical properties, on the nature of their combinations and on 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 pamphlet entitled “An Experimental System of the Ele ments based on their Atomic Weights and Chemical Analogies”, and then in the

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following March, at a meeting of the Russian Chemical Society which he had done so much to organise in the previous year, and with Zinin presiding, a paper from Mendeleev was read by his friend and colleague Professor Nikolai Mens- chutkin because the author had been taken ill. This was published in the first volume of the Society’s transactions (15), and was briefly referred to in the German periodicals, giving their readers some indication of Mendeleev’s ideas. It was not, however, a complete periodic table as we know it but rather a pre liminary study in which he merely arranged the elements in six columns and, as he later emphasised, he was unaware of the publications of Meyer and Newlands and only of Odling’s first communication of 1857 and Lenssen’s even earlier work. As with his predecessors, Mendeleev had difficulties with the platinum group of metals on account of their close similarity and the very small differences in their atomic weights as then determined. In this first system he arranged them: Rh 104.4 Pt 197.4 Ru 104.4 Ir 198 Pd 106.6 Os 199 In a second paper read to a meeting of Russian scientists in Moscow in August 1869, “On the Atomic Volume 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 assumed the presence of an empty period between the ruthenium and the osmium groups. Then in 1870 Lothar Meyer contributed a paper to Liebig’s Annalen, “The Nature of the Chemical Elements as a Function of their Atomic Weights”, (17) in which he arranged the platinum metals in their correct order but with some uncertainty: Ru 103.5 Os 198.6? Rh 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 paper of Meyer’s, Mendeleev published a further account of his system a year later, and this was translated in full in the Annalen (18). Running to almost a hundred pages in the German version, this gave a much clearer and more comprehensive description of his periodic system - the first time he actually used the phrase - and dealt at length not only with the properties of the elements but also with their compounds. More courageous than

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I>jnna I. rp jn n » 11. r|ijuna HI- rp jn n » IV. r|ijont V. Tpinn* VI. rpjnna VII. rpjan* VIII. n rfja I, H =1 1 Tat>a*teeaie u e - MCHru. L i= 7 B*=9,4 B—11 C =12 H = l . 0 = 1 « F = 1 9

5 * | P i n 1-i N i= 2 3 ■ «= *4 A l= 27,3 P = 31 8 = 3 1 C 1=36,4

- i « K =39 C a=40 - = 4 4 Ti=5»>? V=S1 ¡Cr=32 M n=M Fe—5«, Co=69, Ni=5®, Cu=63 (Ouz=63) Zn=6ft - =_68 - = 7 2 Ac = 75 S e= 7 8 Br=8<) i f f - 3 “ i l l Rb=85 S rz 87 (?Y t=88?) Zrrz90 N b -9 4 Mu—»6 -=lttl Rn=104,Ru=104, Pd=H»4,Af=l08 (**-=106) LU—»11 la =113 Sn=118 Sb=132 Te*_l28? J —127 5 j l - M i l l - 6-1 C*=133 Ba—137 - =137 C —-I38? - 1

hi : : : - —- T «= 1 8 2 W - 184 0»=lt*9?,Ir=198?, r 1*1=197, A ii =197 ill - 9-" (A n = J9 7 j H|T=*Jf. T l=204 P b = * l7 Bi=2U8 - - 111 - HW> - - T h rr132 — L’r= 2 4 0

B ucuiai c o j h h m OBIICb. K * 0 R’O* ajm KO R*0* RH)‘ a ja HO* «»O' R’O- m i RWI K'O’ 11*0- i i j « RO* Bucioee ao*o- i poxnoe coejaaeine. (RH*?) RH‘ RH* RH* RH

The revised and comprehensive Periodic Table published by Mendeleev in the Journal of the Russian Chemical Society in 1871. The platinum metals were now placed in their correct order in Group VIII, although this also included copper, silver and gold. A space was left for as yet undiscovered members of the platinum group between the lighter and the heavier triads and the atomic weights were given only in round figures because of Mendeleev's uncertainty about their accuracy

Lothar Meyer, he ascribed different atomic weights to a number of elements, based solely upon their chemical analogies, calling for new determinations 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”.

Mendeleev’s table of 1871 is reproduced here from the original Russian version. It will be seen that in addition to iron, cobalt and nickel and to the platinum metals he had included copper, silver and gold in Group VIII but had left alternative positions for them in Group I, and that, unaware of most of the rare earth elements, he had again left gaps for an extra series between the two

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Karl Friedrich Otto Seubert 1851-1921

The son of a Professor at the Karlsruhe Technische Hochschule, Seubert first studied pharmacy there and then turned to chemistry, serving for several years as assistant to Lothar Meyer and accompanying him to Breslau and then to Tübingen over a period of twenty years and succeeding him as Professor. His doctoral thesis was on the atomic weight of iridium and he went 011 to re-determ ine the atomic weights of all the other platinum metals, confirming the order in which Mendeleev had placed them

platinum metal triads. This had the inevitable result of prompting the re examination of native platinum for the apparently missing elements and led to a number of “ discoveries” that 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 germanium, scandium, gallium, rhenium and technetium. In this table Mendeleev separated the elements into their main and sub groups, while he also confined his atomic weights to round numbers as he could not be sure of their accuracy. His predictions about the correct order for the platinum metals were fully confirmed a few years later by Karl Seubert (1851-1921), a student and later a colleague of Lothar Meyer’s at Tiibingen. Seubert also distrusted some of the old values and set about their re determination, arriving at the following arrangement and so confirming Mendeleev’s views (19): Ru 101.4 Rh 102.7 Pd 106.35 Os 190.3 Ir 192.5 Pt 194.3

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Some Spurious Platinum Metals Several supposedly new elements of the platinum group were claimed before the publication of Mendeleev’s Periodic Table, but the gaps he left, as already mentioned, led to further claims for the isolation of further members of the group. In 1877 Sergius Kern of the Obouchoff Steel Works in St. Petersburg wrote to Chemical News that he had “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 Humphry Davy” (20). This claim was investigated in 1898 by Professor J. W. Mallet, an Irish chemist who had settled in America to become Professor of Chemistry at the University of Virginia, and who thought this might indeed be a member of the missing triad of platinum metals. While he was able to confirm Kern’s experimental observations, he quickly showed that the new metal 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, Antony Guyard 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). The atomic weight was given as 187.25, its specific gravity as 20.25 and its ductility was said to be greater than that of platinum, but the experimental work was of a very low order and ouralium was again almost certainly a mixture of platinum with some iridium and rhodium. These two fallacious discoveries, together with several others, were reviewed in more detail by Dr. W. P. Griffith in 1968 (23).

The Modern Periodic Table Mendeleev continued for the remainder of his life to take an active interest in his Periodic Law and used it as a base in his famous text-book, The Principles of Chemistry, first published in Russia in 1869 and in many later editions, with an English translation in 1891 and German and French versions a few years later. His chapter on the platinum metals opens with a statement of “the naturalness of the transition” from zirconium, niobium and molybdenum to silver, cadmium and iridium through ruthenium, rhodium and palladium, and similarly from tantalum and tungsten through osmium, iridium and platinum to gold and mercury. This is followed by an account of the chemistry of the platinum metals that would have been creditable to an author many years later, as for that matter would the whole of the book. But it was not until the discovery of the electron by Sir J. J. Thomson in 1879 and then Moseley’s work on the X-ray spectra of the elements that led to the concept of atomic number just before his death in 1915 in the European War that a sound theoretical basis could be established for the periodic system.

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The Platinum Metals and their Neighbours in the Periodic Table

Group VIA Group VIIA Group VIII Group IB

First long period C r24 M n 25 Fe26 Co 27 Ni28 Cll 29

Second long period M o42 T c 43 R u 44 R h 45 Pd46 Ag47

Third long period w74 R e 75 0S76 Ir77 Pt78 Au 79

The part of the modern table in which the platinum metals occur is reproduced above with their atomic numbers, this including of course rhenium discovered in 1925 and predicted by Mendeleev as dri-manganese, and technetium, his eka-manganese, discovered only in 1937 in the bombardment of molybdenum by deuterons in a cyclotron. Just as Mendeleev emphasised, the greatest similarities are found in the vertical groups; there is a strong resemblance between ruthenium and osmium, between rhodium and iridium, and between palladium and platinum. At the same time there are obvious analogies in the horizontal series, between for example palladium and silver and between platinum and gold, while ruthenium and osmium more closely resemble technetium and rhenium, or in certain respects molybdenum and tungsten, than they do iron. Rhodium and iridium are more closely allied to cobalt than to any other metal, while platinum and palladium have close analogies with nickel. In the two platinum metal triads the hardness and mechanical strength decrease from left to right and are greater in the second triad than in the first. Ruthenium and osmium, both close-packed hexagonal in crystal structure are brittle although they can be fabricated with difficulty at high temperatures, 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 the group was contributed some years ago by the writers’colleague A. R. Powell (24).

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References for Chapter 18

1 A. M. Ampère, Ann. C him , 1816, 1, 295-308; 2, 5-32 2 J. W. Dobereiner, Ann. Phys. ( Poggendorff), 1829, 15, 301-307 3 J. H. Gladstone, Phil. Mag., 1853, 5, 313—320 4 E. Lenssen, Ann. Chem. ( Liebig), 1857, 103, 121-131; 104. 177-184 5 W. Odling, Phil. Mag., 1857, 13, 422-^39; 480-497 6 H. Sainte-Claire Deville and H. Debray, Ann. Chim., 1859, 56, 385-389 7 C. Claus, J . prakt. Chem., 1860, 79, 28-59; 80, 282-317; Chem. News, 1861, 3, 194-195; 257-258 8 M. Faraday, A Lecture on Platinum, bound with The Chemical History of a Candle, London, 1861, 173-204; Chem. News, 1861, 3, 136-141 9 W. Odling, A Manual of Chemistry, Part 1, London, 1861, 3 10 J. A. R. Newlands, Chem. News, 1863, 7, 70-72; 1864, 10, 59-60; 94-95; 1865, 12. 83 11 J. A. R. Newlands, On the Discovery of the Periodic Law, London, 1884 12 W. Odling, Q_.J. Sci., 1864, 1, 642-648 13 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 14 J. L. Meyer, Die modernen Theorien der Chemie, Breslau, 1864 15 D. I. Mendeleev, ^[hur. Russ. Khim. Obshch., 1869, 1, 60-77 16 D. I. Mendeleev, Proc. 2nd Meeting Scientists, 23 Aug, 1869, 62-71 17 J. L. Meyer, Ann. Chem. ( Liebig), 1870, Supp. VII, 354—364 18 D. I Mendeleev, %hur. Russ. Khim. Obshch., 1871, 3, 25—56; Ann. Chem. ( Liebig), 1871, Supp. VIII, 133-229 19 K. Seubert, Ann. Chem. ( Liebtg), 1891, 26 1, 272-279 20 S. Kern, Chem. News, 1877, 36, 4; 114-115; 164 21 J. W. Mailet, Am. Chem.J., 1898, 20, 776 22 A. Guyard, Moniteur Scientifique, 1879, 9, 795-797 23 W. P. Griffith, Chemistry in Britain, 1968, 4, 430^134 24 A. R. Powell, Platinum Metals Rev., 1960, 4, 144-149

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Henri Louis Le Chatelier 1850-1936 Born in Paris. I,e Chatelier spent some time under Sainte-Claire Deville at the Ecole Normale but his education was interrupted by the Franco/Prussian War. I.ater he studied at the Ecole des Mines and became a mining engineer but in 1877 he returned there to teach chemistry, being appointed Professor ten years later. He was the first to employ a platinum against rhodium-platinum alloy thermocouple, so initiating a reliable means of determining high temperatures