Red Barium Cobalti-nitrite, 2BaO.Co₂O₃.4N₂O₃

On passing nitrous oxide into a suspension of cobalt carbonate in a solution of the requisite quantity of barium nitrite a deep red solution is first formed. This is filtered off before the whole of the cobalt carbonate has dissolved, and evaporated over sulphuric acid at room temperature. At first a little of the yellow barium cobalti-nitrite separates out, but finally deep red crystals of Red Barium Cobalti-nitrite, 2BaO.Co₂O₃.4N₂O₃.10H₂O, are obtained, appearing grey-violet by reflected light under the microscope. The crystals cannot be redissolved in water.