 Treatment of hexachloroplatinic acid with an ammonium salt , such as ammonium chloride , gives ammonium hexachloroplatinate , which is relatively insoluble in ammonium solutions . Heating this ammonium salt in the presence of hydrogen reduces it to elemental platinum . Potassium hexachloroplatinate is similarly insoluble , and hexachloroplatinic acid has been used in the determination of potassium ions by gravimetry . 
