Platinum

Platinum is ductile and malleable and has a coefficient of expansion similar to soda-lime-silica glass, so it is used to make electrodes in sealed glass.   Like gold, platinum is insoluble in hydrochloric acid and nitric acid, but it is dissolved by the combination of the two acids, as aqua regia to form chloroplatinic acid, H₂PtCl₆, used as a catalyst and for other applications.   Platinum is used in jewelry, wire, laboratory vessels, thermocouple contacts, electrical contacts, corrosion-resistant apparatus, and dentistry.   Platinum-cobalt alloys have strong magnetic properties that are useful industrially.   Platinum resistance wires are used in high-temperature electric furnaces.   Platinum coatings are used in missile nose-cones, jet engine fuel nozzles, and other places where reliability is required at high-temperatures for long time periods.   In a fine powder state, platinum is used as a catalyst in the production of sulfuric acid and in petroleum refining.   Platinum anodes are used in cathodic protection systems for large ships, pipelines and piers.   Fine platinum wire placed in methyl alcohol vapor will glow red hot where it acts as a catalyst to convert the alcohol to formaldehyde.   This reaction is used to produce cigarette lighters and hand warmers. ^{Lide 4-21}

Platinum was used by the pre-Columbian Amerindians.   It was rediscovered by Ulloa (S.America) in 1735 and by Wood in 1741.   It was impractical to use until William Hyde Woolaston, a British chemist, invented a method to work and pound it into shape in 1800. ^{Asimov 282}   Platinum occurs in free form, accompanied by small amounts of iridium, osmium, palladium, ruthenium and rhodium, which all belong to the same chemical family.   Sperrylite, PtAs₂, contains much platinum, along with nickel. ^{Lide 4-21}