The Wollaston Medal was worth £ 1.50;
1847: 1 Troy Ounce Platinum (refined) = £ 1.60 (USD$ 7.66)
1847: 1 Troy Ounce Palladium (refined) = £ (USD$ )
c.1840:
Citation: The practical metal-worker's assistant ...: With the application of the art ... By John Scoffern, William Clay, Sir William Fairbairn, James Napier (1851) p. 196.
The impurity of Palladium was a concern to dentists. The suggestion that it was never used is somewhat dubious and contradicts other sources.
Citation: The Principles and practice of dental surgery, By Chapin Aaron Harris, (1858) p.758
Citation: Platinum Metals Rev., 1991, 35, (3)
...it was certainly known in Paris in the late 1770s. Be that as it may, appended to the paper was a note of considerable interest and significance. In this, Johnson and his father reported that some gold arriving from Brazil contained so much palladium that the colour was changed, and that coins made from it were suspected as being counterfeits.
In due course Peruval Norton Johnson moved to Hatton Garden and built up the business that was to become Johnson Matthey. But before this happened, Johnson was contracted to refine the gold brought into London by the Imperial Brazilian Mining Association. This Association had been formed in December 1824 to mine at Gong0 Soco, in the Brazilian province of Minas Geraes, some 180 miles north of Rio de Janeiro.
As had been reported previously by Wollaston, the gold contained a significant amount of palladium, both as particles of native palladium and alloyed with the gold. In the latter, the palladium content varied from, perhaps, one or two up to a maximum of 8.2 per cent. Prior to 1832 the gold was brought to London in the form of crude bars cast at the Government Mint at Sabara, but these contained varying amounts of iron, palladium and tellurium. As a result the bars were discoloured and some were brittle; the latter, being rejected by the Bank of England’s smelters, were unsaleable (33). On the other hand, the non-brittle bars were refined at the Royal Mint but the process resulted in the loss of all the palladium. After 1832, however, the export of gold from Brazil in the form of powder was permitted, and by this time Johnson had “discovered the means of separating from the gold all the metals in combination with it, and which consist of silver, platina, palladium, rhodium and iridium.. ..palladium is a metal but little known, and is found to be most valuable in the construction of astronomical, nautical and experimental instruments, being perfectly free from all oxydation, and quite malleable, and will no doubt increase in value as its qualities become more generally understood.” (34)
Indeed, his success in refining this difficult gold, which contained tellurium in addition to palladium, “led eventually to the full recognition of his fim as refiner and their appointment as Assayers to the Bank of England.” (35) More immediately, as a result of his scientific investigations and his accumulated technical skills, Johnson was able to add significant value to the ore imported by the Imperial Brazilian Mining Association.
As Wollaston had found, applications for the recovered palladium did not develop rapidly. In July 1823, Aime Puymaurin, then Deputy Director of the Paris Mint, wrote a paper detailing the properties of palladium, as determined by Jean Robert Breant, one of the assayers at the mint. He had undertaken the refining of 1000 kilogrammes of Spanish platina from which he had recovered some 900 grammes of palladium. Breant used part of this palladium to strike a medal which he presented to Louis XVIII of France; then in 1824 when King Charles X succeeded his brother, Br6ant presented him with an ornate cup consisting of a palladium bowl mounted on a silver base (36).
In an attempt to identify further industrial applications, Johnson also sought to promote a greater awareness of palladium by making suitable presentations. For example, in 1826 a massive ceremonial chain made of palladium was presented to King George IV (37). The promotional exercise lasted at least until 1845, when Johnson presented to the Geological Society sufficient palladium to make their prestigious Wollaston Medal for several years. In time such early uses as for the scales of scientific and astronomical instruments, reflectors for lighthouses, analytical weights, jewelery, and for dental purposes, were supplemented by medical and electrical contact applications, and uses based upon the remarkable ability of palladium to absorb vast amounts of hydrogen.
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