Iridium sesquioxide, Ir 2 0 3, is obtained when potassium iridium chloride is heated with sodium or potassium carbonates, in a stream of carbon dioxide.
It is a strong acid, and dissolved in water decomposes carbonates and attacks iron and zinc.
Heated with sulphuric acid and with nitric acid it is oxidized to boric acid, whilst on fusion with alkaline carbonates and hydroxides it gives a borate of the alkali metal.
In Western Australia the lead occurs in the form of sulphides and carbonates of great richness, but the quantity of silver mixed with it is very small.
Zinc ores, in the several varieties of carbonates, silicates, oxide, sulphide and sulphate of zinc, have been found in several of the Australian states, but have attracted little attention except in New South Wales, where special efforts are being made successfully to produce a high-grade zinc concentrate from the sulphide ores.