Nickelo-nickelic Oxide, Ni₃O₄

Tri-nickel Tetroxide, Nickelo-nickelic Oxide, Ni₃O₄, results when nickel chloride is subjected to prolonged heating at 440° C. in moist oxygen. In appearance it is grey and metallic.

The oxide may also be obtained in the dihydrated condition, Ni₃O₄.2H₂O or NiO₂.2NiO.2H₂O, by fusing sodium peroxide with metallic nickel and removing the alkali by thorough washing, when it is formed as dark crystals which dissolve in acids yielding salts of divalent nickel. Density 3.412 at 32° C. On heating to redness nickel monoxide is formed.

Nickel Sesquioxide, Nickelic Oxide, or Nickelous Nickelite, Ni₂O₃ or NiO.NiO₂. Frequent references occur in the literature to this oxide, the analogue of ferric and cobaltic oxides. It would appear, however, from the researches of Bellucci, that the substance originally believed to have the above composition is in reality the dioxide, NiO₂, or a mixture of this dioxide with the monoxide (vide infra), and that the sesquioxide has not as yet been obtained. These conclusions were arrived at as the result of studying the action of oxidising agents on nickel sulphate in alkaline solution. It was found that the degree of oxidation depended both on the nature of the oxidising medium and upon the rapidity of oxidation. No arrest was found corresponding to the sesquioxide. Hofmann and Hiendlmaier found that, on burning potassium in nickel vessels exposed to air, black prisms were formed to which they ascribed the formula NiO.NiO₂.K₂O. On washing thoroughly with water, raven-black metallic crystals, of empirical composition Ni₂O₅H₄, were left. These readily oxidised organic matter, and the authors suggested the formula NiO.NiO₂.2H₂O. The sodium salt, NiO.2NiO₂.Na₂O, has also been prepared. Upon hydrolysis it yields the same hydrated oxide, Ni₃O₄.2H₂O.