Complex sentence: Dissolving platinum solids in aqua regia was the mode of discovery for the most dense metals, iridium and osmium, both of which are found in platinum ore and will not be dissolved by the acid, instead collected on the base of the vessel.
Split into simpler sentences: Dissolving platinum solids in aqua regia was the mode of discovery for the most dense metals. Iridium and osmium, both of which are found in platinum ore and will not be dissolved by the acid, instead collected on the base of the vessel.