Platinum
Pure platinum is a lustrous, ductile, and malleable, silver-white metal. Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals, but it is less malleable than gold. The metal has excellent resistance to corrosion, is stable at high temperatures and has stable electrical properties. Platinum does oxidize, forming PtO, at 500 °C; this oxide can be easily removed thermally. It reacts vigorously with fluorine at to form platinum tetrafluoride. It is also attacked by chlorine, bromine, iodine, and sulfur. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot "aqua regia" (A mixture of nitric and hydrochloric acids), to form chloroplatinic acid, HPtCl.
Cyril Stanley Smith
But by far the biggest challenge for Smith and his group was plutonium, a metal hitherto available only in microgram amounts, and whose properties were largely unknown. It was initially assumed that plutonium would have properties similar to that of uranium, but this assumption turned out to be invalid. Plutonium proved to be "the most complicated metal known to man". There were found to be six allotropes of plutonium, more than any other metal, and its melting point turned out to be hundred of degrees lower than uranium. The metallurgists found that at around 125 °C, plutonium expanded in volume by 20 percent, which is unusual.