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.
Three characteristic oxides of cobalt are known, the monoxide, CoO, the sesquioxide, C0203, and tricobalt tetroxide, C0304; besides these there are probably oxides of composition Co02, Co 8 0 9, C0607 and C0405.
Cobalt sesquioxide, Co 2 0 3, remains as a dark-brown powder when cobalt nitrate is gently heated.
The barium and magnesium salts of this acid are formed when baryta and magnesia are fused with cobalt sesquioxide.
The ore generally occurs in the form of oxides, manganite and pyrolusite, and contains a high percentage of sesquioxide of manganese.