Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Tetraboron pentoxide, B4O5

Tetraboron pentoxide, B4O5, is prepared by treating the compound Mg3B2(OH)6 with strong ammonia for several days in an atmosphere of hydrogen, filtering, evaporating the filtrate to dryness in vacuo, and heating the residue. Thus prepared, it forms a pale brown solid, infusible at the softening point of Jena glass. When allowed to remain in vacuo in contact with water it dissolves, forming a golden-yellow solution that oxidises rapidly in the air; a small flocculent residue, apparently consisting of B4O3.2H2O, is also obtained. It is possible that the residue is produced by the following reaction: -

3B4O5 = B4O3 + 4B2O3.

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