Red Sodium Cobalti-nitrite, 2Na₂O.Co₂O₃.4N₂O₃

To obtain Red Sodium Cobalti-nitrite, 2Na₂O.Co₂O₃.4N₂O₃, nitrous acid is added to a suspension of cobalt carbonate in the requisite quantity of sodium nitrite solution until a reddish brown colour is attained. The liquor is evaporated by exposure over sulphuric acid, leaving a reddish brown crystalline powder of the above composition. Alcohol does not precipitate this salt from its aqueous solution, neither is a precipitate obtained with a soluble potassium salt. In both these features, therefore, the red sodium cobalti-nitrite differs from the yellow salt already described. Continued treatment with nitrous oxide converts the red salt into the yellow derivative.