Platinum Metals Rev., 1966, 10, (3), 101
William Hyde Wollaston
The Production of Malleable Platinum
The occurrence of the bicentenary of Wollaston’s birth affords an opportunity to review in these pages the important scientific and technical work that he did in the field of the platinum group of metals. The physical and chemical details of that work are of course well known from his published papers to the Royal Society, including the Bakerian Lecture of 1828 which he prepared just before his death. But, until recent years, little was known about the circumstances in which he undertook and carried on the work and a number of legends have grown up about it. These have latterly been dispersed, and the true facts brought to light, by the long and painstaking work of the late Mr L. F. Gilbert, who devoted many years to a study of the subject but unfortunately died before he could collate and publish the results in full. He was, from 1919 to 1955, a lecturer in chemistry at University College, London, and his papers are in the custody of its Library, but have not so far found an editor to prepare them for the publication for which those interested have hoped. He did, however, in 1952 publish a short paper on Wollaston’s work on platinum in The Notes and Records of the Royal Society which, together with a long correspondence over many years with the writer of this article, helped to disclose a number of facets of the affair. It is possible therefore to incorporate a good many of Gilbert’s conclusions here.
Wollaston was born in Norfolk on August 6th, 1766, the third son of Francis Wollaston and his wife, Althea Hyde. His father was an astronomer and one of his uncles a well-known doctor, William Heberden; both were Fellows of the Royal Society. His main schooling was at Charterhouse (1774–78) and in July 1782 he was admitted to Gonville and Caius College, Cambridge, to study medicine with a view to making a career in it. He graduated M.B. in 1787 (M.D. in 1793), was awarded a Fellowship and stayed on for two years.
While there, he met fellow students with interests in the pure sciences and became attracted by their work. He tried his hand at astronomy and botany, but it was chemistry and physics that appealed to him most and in 1786 he took up serious study in them under Isaac Milner. In this course he was no doubt stimulated by his friendship with Smithson Tennant, a well-to-do young Yorkshireman who had been at Christ’s reading chemistry and botany since 1782, and had just (1786) transferred to Emmanuel, and was already (1785) a Fellow of the Royal Society. He was five years older than Wollaston and had been to the Continent and met leading chemists there. This experience had made him a clever experimenter and Wollaston was fascinated by the results. He did some work himself in his own rooms and in the laboratory of his brother, Francis, also studying at Cambridge, and so were laid the foundations of his scientific knowledge and the openings for his own genius in experiment.
In 1789 he moved to London to forward his medical studies by attending lectures and walking the hospitals and eventually, in 1792, he took up practice at Huntingdon. This lasted only a few months and he moved to Bury St Edmunds, where he stayed until 1797, becoming qualified as a Fellow of the Royal College of Physicians in 1793. He was popular in his district and had a full programme of social engagements, but still found time for the study of nature. In 1797 his friends persuaded him to move to the wider scope of London and then, in 1800, to the surprise of everyone, he threw up his practice and retired from medicine.
Work with Smithson Tennant
His reasons for doing this have been much debated but there seems to be no reason to doubt his own statement that mental anxiety about his patients caused him excessive and painful distress. At the same time there had opened for him some hopes of being able to make beneficial use of his experience in chemical research, which he was tempted to develop in association with his friend Smithson Tennant. The latter had also prepared himself to practice medicine but he too had given it up, though for reasons different from those that affected Wollaston. Tennant was casual in his approach to life and had inherited sufficient money to support himself; Wollaston was serious and steadfast but had to earn his living. The combination of the two had the promise of being effective and they duly came together for business, turning their attention to the preparation of platinum for commercial and scientific use, a subject that had already attracted the attention of both in the laboratory.
To explain their reasons for choosing it and to emphasise the importance of their work, it is necessary to give some attention to past history. Until well into the present century it was generally believed that Wollaston alone was the pioneer in making platinum available for fabrication. The leading chemical textbook of the turn of the century (Roscoe and Schlorlemmer) mentions a few earlier names but gives little indication that their work was of any importance; nothing was then known about Tennant’s part in the business until Gilbert discovered it in the 1930s through access to the accounts. On the other hand, Wollaston’s scientific results were completely documented in the Bakerian Lecture. But in this he makes little reference to his predecessors, none to his collaborators and none to the use to which his process was put. He did however in another place make a public statement that he made no claim to have originated it, but merely to have improved its details.
Platinum Fabrication before Wollaston
Native platinum was first brought to the notice of European scientists in 1748 after occasional rumours of its existence in New Granada. As soon as samples were available a number of well-known chemists got to work upon it and by 1760 a great deal had been found out. Naturally its powers of resistance to melting at the highest temperatures then available and to corrosion by all the simple acids soon gave rise to hopes of using it. The French chemist Baume produced evidence that it could be consolidated by forging at a high temperature like iron, but it was soon found that when this was applied to the grains of the native metal they often failed to cohere. This was due to the fact that the mineral contained a small quantity of alloyed iron and, at the very high temperature used, this oxidised to a surface film of magnetite. To secure bonding, therefore, this iron must be removed. The first process used was a scorification of the mineral with an oxidising mixture of potash and white arsenic. This not only removed the iron, but yielded a molten eutectic product that could be cast into thin discs from which, by careful heating just below the melting point, the arsenic could be volatilised and the resulting medallion forged to good malleable metal. This method was exploited by the French goldsmith Janety over the period 1786 to 1812 and by its aid he made jewellery, crucibles and other laboratory ware. The principal example of his work that has survived is the four original Standard Metres, all of which are still preserved in Paris.
The arsenic process was slow, painful and dangerous, and alternative methods were at once sought. These concentrated on dissolving the mineral in aqua regia, precipitating the platinum with sal-ammoniac, calcining this to a sponge of platinum metal, heating this to the highest temperature possible and then forging the product. This too was developed in France by a series of distinguished chemists of whom the last, de Milly, communicated the details to Fausto de Elhuyar in Spain, who had been encouraged by his Government to study possible uses for this Spanish-American product. Don Fausto soon produced a workable process (1786) in conjunction with a French colleague, Pierre Chabaneau, but had then to go to other duties, leaving the latter to put it to commercial use. A laboratory-factory was set up for him in Madrid and between 1786 and 1804 a considerable amount of refined malleable platinum was turned out in ingots, jewellery, objets d’art and chemical apparatus. A surviving example of the work of Chabaneau’s silversmith Francisco Alonso is the splendid 55-ounce platinum chalice dated 1788 given by the King of Spain to Pope Pius VI and preserved in the Treasury at St Peter’s, Rome.
It is apparent therefore that considerable quantities of reasonably good malleable platinum had been prepared and used well before 1800. But the methods used were purely empirical, the product varied in quality and sometimes failed mechanically. There was no real fundamental knowledge of the composition of the native mineral or of the nature and properties of the products derived from it. At its best, the principal one reasonably satisfied a need and no notable progress was made until Wollaston and Tennant decided to seek it.
In 1798 in London the newly founded Philosophical Magazine published an English translation of some recent French work on platinum by the Abbé Rochon and this revived in England an interest in the metal that had flagged since the classic work of Lewis forty years earlier. At least three people were stimulated to do some work on the subject. The first was Richard Knight, who sent a paper to the Philosophical Magazine in 1800 on a new method for making the metal malleable. In it platinum sponge was prepared as his predecessors had done but, before forging, he compressed it by hand-pressure into a white-hot mould and only applied the hammer after this had been done. The second interested party was William Allen, the famous pharmacist who, with a young assistant named Thomas Cock, took up the study a year or two later. This resulted in the production of some crucibles in 1805 but nothing was known about the methods until Cock published them in 1807. Then it was disclosed that the sponge metal was now pressed in a cold mould, first by hammering and then by means of a screw press. Only after that was heat applied and forging begun. This method was later applied industrially by Cock’s brother-in-law, Percival Johnson, the founder of Johnson Matthey & Co. Meanwhile the third interested party in 1800 comprised Wollaston and Tennant.
They entered into a loose partnership to investigate thoroughly native platinum from the scientific point of view and then to develop its industrial uses. According to Gilbert, at the beginning they shared expenses until earnings began to come in to help with them. Profits did not appear until 1809 but then improved rapidly; Wollaston as working partner was allowed 10 per cent of income before the rest was equally divided. The partnership continued until Tennant’s death in 1815, after which Wollaston continued the work alone until 1821 when it seems to have ceased. In all, from 1800 to 1821, about 47,000 troy ounces of native platinum were treated and nearly 36,000 ounces (over one ton) of malleable platinum obtained. The first operations were purely scientific. Between 1800 and 1803, 7000 ounces of native metal were dissolved in aqua regia and Wollaston devoted himself to an intensive examination of the solution, while Tennant inquired into the relatively small quantity of insoluble black material which had hitherto been dismissed as ‘graphite’. The result was that Wollaston discovered palladium and rhodium, and Tennant iridium and osmium. This cleared the way for work on the solution and, by February 1805, five crucibles had been made and sold, the price being 5s per ounce. But the really important sales came from a new use introduced by Wollaston, namely, the manufacture of boilers for concentrating the weak sulphuric acid, produced by the chamber process, to oil of vitriol. Between 1805 and 1818 there were sixteen of them, weighing from 322 to 427 ounces (24 to 47 wine gallons) at prices up to £400. Nearly 7000 ounces of metal were sold in this form, against 1300 ounces for crucibles, and Gilbert gives a surprising figure of 17,000 ounces as going to gun-makers, ostensibly for touch-holes but probably for decoration as well.
As mentioned above, Wollaston published a full account of the technical details of his process just before he died in 1828. The essential points are that the aqua regia used for dissolving the mineral should be dilute (about 50:50) to avoid dissolving the iridium. The yellow precipitate produced by salammoniac was to be well washed and then well pressed, before being gently heated at a low heat to produce platinum sponge. He emphasised that the heat must be only just enough to bring this about and, in any grinding required, the metal must on no account be burnished. He recognised the need to preserve in the sponge a certain virginity about its surfaces if the subsequent welding was to be successful. A century later his acumen in this respect provided a vital foundation for the science of powder metallurgy. Having got his sponge into a fine and uniform powder by hand-rubbing, he washed and elutriated it thoroughly with water. After pouring off the excess of this, he transferred the metal mud to a brass mould and then closed this with a steel stopper wrapped in blotting-paper and topped with some wool, which allowed the excess water to escape under hand-pressure. A plate of copper was then put on top and the whole introduced into a powerful horizontal press of his own design. This produced a hard cake of metal which was next exposed to the greatest heat that he could obtain and then forged by hand on an anvil. An ingot of about 20 oz of malleable platinum resulted and this could be hammered into sheet or drawn into wire. Such was the material which Wollaston and his fabricators used for their articles for sale. He himself used the full procedure throughout the rest of his working life, but his successors never took up the wet part of the process, preferring to follow Knight and Cock in compressing the sponge in a dry state before forging it. Perhaps for this reason the properties of their metal were never quite as good as Wollaston’s, but nevertheless it was good enough to satisfy their clients until well into the present century. The rest of his discoveries they were very pleased to adopt, and the platinum fabricating industries of both England and France used them to improve their existing methods. But really it was not until a century after Wollaston’s start of his work that the real significance of his investigations into the properties of the surface of powdered metals was grasped and applied to the beginnings of powder metallurgy.
In his obituary notice in the Gentleman’s Magazine of 1829 the statement is made that “his discovery of the malleability of platinum it has been asserted, alone produced about £30,000”, and this story has been freely exploited by later writers. Gilbert, with his access to Wollaston’s accounts, reduces the figure by about half, and that from all his business activities. It does seem, however, that he did achieve his object of financing his research activities by means of this work. Gilbert describes its scope as extending “inter alia to optics, astronomy, crystallography, mineralogy, electricity, mechanics, physiology and pathology, nearly all his clear and concise papers giving useful, often classical, additions to knowledge”. He invented valuable optical instruments, gave early support to the new atomic theory, and made important discoveries in the directions of stereochemistry, spectroscopy, electromagnetic induction, refrigeration, photography and the above-mentioned powder metallurgy. Charles Babbage said of him that in his mind there was “a plain and distinct line which separated what he knew from what he did not know”, and “that his predominant principle was to avoid error”. His contribution to the advancement of science was a very large one.