____|________|________|_________|_________ |__________|_____________
| | | | | |
Ruthenium | Ru | 101.7 | 12.26 | RuO_{4} | RuCl_{4} | Electric arc
Rhodium | Rh | 103. | 12.1 | RhO_{2} | RhCl_{2} | Electric arc
Palladium | Pd | 106.5 | 11.8 | PdO_{2} | PdCl_{4} | 1500 deg.
Iridium | Ir | 193. | 22.42 | IrO_{2} | IrCl_{4} | 1950 deg.
Osmium | Os | 191. | 22.47 | OsO_{4} | OsCl_{4} | Electric arc
Platinum | Pt | 194.8 | 21.50 | PtO_{2} | PtCl_{4} | 1779 deg.
Gold | Au | 197.2 | 19.30 | Au_{2}O_{3} | AuCl_{3} | 1064 deg.
==============================================================================

~The family.~ Following iron, nickel, and cobalt in the eighth column of
the periodic table are two groups of three elements each. The metals of
the first of these groups--ruthenium, rhodium, and palladium--have
atomic weights near 100 and densities near 12. The metals of the other
group--iridium, osmium, and platinum--have atomic weights near 200 and
densities near 21. These six rare elements have very similar physical
properties and resemble each other chemically not only in the type of
compounds which they form but also in the great variety of them. They
occur closely associated in nature, usually as alloys of platinum in the
form of irregular metallic grains in sand and gravel. Platinum is by far
the most abundant of the six.

Although the periodic classification assigns gold to the silver-copper
group, its physical as well as many of its chemical properties much
more closely resemble those of the platinum metals, and it can he
conveniently considered along with them. The four elements gold,
platinum, osmium, and iridium are the heaviest substances known, being
about twice as heavy as lead.

PLATINUM

~Occurrence.~ About 90% of the platinum of commerce comes from Russia,
small amounts being produced in California, Brazil, and Australia.

~Preparation.~ Native platinum is usually alloyed with gold and the
platinum metals. To separate the platinum the alloy is dissolved in aqua
regia, which converts the platinum into chloroplatinic acid
(H_{2}PtCl_{6}). Ammonium chloride is then added, which precipitates the
platinum as insoluble ammonium chloroplatinate:

H_{2}PtCl_{6} + 2NH_{4}Cl = (NH_{4})_{2}PtCl_{6} + 2HCl.

Some iridium is also precipitated as a s