Wollaston and Tennant experimented on platinum ore, discovering the new elements and developing techniques for producing powdered platinum and a malleable, purified platinum metal. Following Wollaston’s death, his friend Percival Johnson utilized the same technique for industrial production of platinum, founding the Johnson and Matthey Company, which remains a major producer of platinum group metals.

Archaeologists have discovered platinum inlays in ancient Egyptian tombs. Indigenous peoples in northern Ecuador and Colombia also used the metal, developing methods of sintering platinum to manufacture jewelry around 400 c.e. They continued utilizing platinum until they were conquered by the Spanish in the sixteenth century. Europeans first encountered platinum when Spanish scientist Antonio de Ulloa Ulloa, Antonio de rediscovered platinum in the form of alluvial “platina” pebbles in the Rio Pinto in Colombia in 1735. Platinum was viewed by the Spaniards as a contaminant in the processing of gold, as it caused metallic gold to become brittle and difficult to refine: They forbade its export to Europe. [kw]Wollaston Begins His Work on Metallurgy (1797)
[kw]Metallurgy, Wollaston Begins His Work on (1797)
Metallurgy
[g]England;1797: Wollaston Begins His Work on Metallurgy[3290]
[c]Geology;1797: Wollaston Begins His Work on Metallurgy[3290]
[c]Chemistry;1797: Wollaston Begins His Work on Metallurgy[3290]
[c]Science and technology;1797: Wollaston Begins His Work on Metallurgy[3290]
Wollaston, William Hyde
Tennant, Smithson
Johnson, Percival Norton
Matthey, George

In 1745, de Ulloa was detained by the British Royal Navy while en route to Spain, and his notes were temporarily confiscated. De Ulloa was taken to London, where he was befriended by British scientists and made a member of the Royal Society in 1746. British scientists began to study de Ulloa’s platina pebbles, and in 1750, William Brownrigg Brownrigg, William presented evidence to the Royal Society that they were composed of a new metal, “platinum.” Platinum By 1783, French scientist François Chabaneau Chabaneau, François was able to produce a malleable platinum ingot.

While a student at Cambridge, Smithson Tennant became interested in platinum metal production. While visiting the chemist Lorenz von Crell in Helmstadt in 1784, Tennant wrote in his diary of learning Count von Sickingen’s method for producing malleable platinum, which involved dissolving the ore in aqua regia (a mixture of one part nitric acid to four parts hydrochloric acid), precipitating out platinum powder, and heating and hammering the powder. Throughout Europe, scientists were hampered by the technological inability to generate enough heat to reach the temperature (1,772° Celsius) needed to melt the metal. An alternative, the process of sintering Sintering —taking a metal powder, compressing it, and heating it until a solid metal piece is formed (which happens at a temperature below the metal’s melting point)—had been known for at least two thousand years.

Tennant and a friend from Cambridge, William Hyde Wollaston, formed a scientific partnership in 1797 to investigate platinum. In late December, 1800, Tennant and Wollaston purchased 5,959 Troy ounces (185 kilograms) of concentrated platinum ore for £795. (Gold and platinum weights are traditionally measured in Troy ounces, rather than the avoirdupois ounces used to weigh most other substances. One Troy ounce equals a weight of about 31.1 grams, as opposed to an avoirdupois ounce, which weighs roughly 28.35 grams.)

Wollaston began treating platina ore with aqua regia to dissolve it. He then added ammonium chloride to the solution, which caused most of the platinum to precipitate. He found that adding zinc caused the residual platinum, some palladium, rhodium, lead, and copper to precipitate as well. Wollaston then took the platinum powder precipitated from his solution, sintered it, and hammered the resulting solid. Using this production technique, now called “powder metallurgy,” Wollaston began marketing metallic platinum in 1805, garnering a profit estimated at £30,000. Tennant shared in the platinum profits until his death in 1815. Wollaston’s malleable platinum was used to producing boilers that could withstand manufacturing highly corrosive sulfuric acid and in fabricating crucibles for use in specialized chemical reactions.

Manipulating platinum led to several ancillary discoveries: Wollaston discovered palladium Palladium sometime before April, 1803, when he offered it for sale as a “new metal” in a Soho shop. He discovered rhodium shortly afterward. Wollaston also found that one by-product of processing platina ore was an insoluble black residue, which he gave to Tennant for further analysis. Studying one hundred Troy ounces of the residue, Tennant first heated some of it with sodium hydroxide and then dissolved the product in water, which yielded an odiferous yellow liquid. When acidified, an odorous white compound, now known as osmium tetroxide, Osmium was produced. Dissolving this white compound in water and adding copper, silver, or zinc, Tennant was able to produce another new element, black metallic osmium.

Tennant recovered iridium Iridium through a complex series of manipulations of osmium. He fused the black powder with caustic soda, used hydrochloric acid extraction to produce a residue that he again fused with caustic soda, and performed a second hydrochloric acid extraction on the second soda-residue fusion. He was left with red crystals, which he heated until he was left with a white powder that he could not melt. Tennant called this powder iridium. Tennant presented his discoveries of osmium and iridium to the Royal Society in 1804.

Between 1803 and 1821, Wollaston, together with his servant John Dowse, Dowse, John processed an estimated 47,000 Troy ounces of platinum ore, recovering 255 Troy ounces of rhodium and 302 Troy ounces of palladium. Wollaston investigated ways to use palladium, making corrosion-resistant sextants and other graduated scientific instruments out of palladium-gold alloys. Wollaston also made rhodium-tin pen nibs in the 1820’s, which were sold for sixpence each.

Wollaston made his platinum production process public one month prior to his death in 1828, along with his technique for producing malleable palladium and pure osmium tetroxide. His friend Percival Norton Johnson continued using Wollaston’s powder metallurgy methods to produce all five of the then-known platinum group metals (PGM). A sixth PGM, ruthenium, was discovered in 1844 by Karl Karlovich Klaus. Klaus, Karl Karlovich

PGMs steadily grew in importance over the nineteenth century, and the Johnson and Matthey Company became the world’s major supplier of these specialty metals and their alloys. By 1867, Johnson and George Matthey had exhibited fifteen thousand Troy ounces of platinum products at an international metallurgical exhibition in Paris. In 1874, platinum-iridium alloys were used to produce standard meter and kilogram measures.

In 1908, Sir William Crookes reported on PGM crucibles that Johnson and Matthey had constructed, having determined that iridium crucibles were as hard as steel, unaffected by mechanical treatment, and resistant to all chemicals except caustic potash. Iridium and iridium-platinum alloy crucibles continue to be manufactured in the twenty-first century.

The physical properties of the PGMs—their resistance to corrosion, high melting points, and roles as catalysts for important chemical reactions—made these metals increasingly important. From their use as catalysts in petroleum refineries to their use in automotive catalytic converters for air pollution control, platinum and palladium are essential to the oil industry. All the PGMs have been used to make electrical contact points because of their resistance to corrosion. Rhodium, ruthenium, iridium, and osmium are often added to the softer and more ductile platinum and palladium to produce a hardened alloy. Iridium has been used as a coating for missile nose cones because of its resistance to heat. Today’s Johnson Matthey Company manufactures rhodium-platinum thermocouples for high-temperature use.

• Cotton, S. A. Chemistry of Precious Metals. London: Blackie Academic, 1997. A monograph concerned with the inorganic chemistry of gold, silver, and the six platinum group metals; contains sixteen hundred references up to the year 1996.
• Griffith, W. P. “Rhodium and Palladium: Events Surrounding Their Discoveries.” Platinum Metals Review 47 (2003): 175-183. Part 1 of a review of the discovery of palladium and its use in metal alloys and as a catalyst in modern air pollution control devices.
• _______. “Osmium and Iridium: Events Surrounding Their Discoveries.” Platinum Metals Review 48 (2004): 182-189. Part 2 of a review of Tennant’s partnership with Wollaston in the study of platinum group metals, including discovery of the elements osmium and iridium in the insoluble black powder produced as a by-product of Wollaston’s platinum purification process.
• McDonald, Donald, and L. B. Hunt. A History of Platinum and Its Allied Metals. London: Johnson Matthey, 1982. An authoritative text on the platinum group metals uses through the mid-twentieth century.
• Tsuji, Jiro. Palladium Reagents and Catalysts: New Perspectives for the Twenty-First Century. Chichester, England: Wiley, 2004. An authoritative text on organopalladium chemistry advances from 1970 to 2003 and the increasingly important role palladium compounds either as stoichiometric reagents or as catalysts in organic synthesis, discusses industrial processes based on palladium-catalyzed reactions.

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